Prosthetic groups are bound tightly to proteins and may even be attached through a covalent bond. They often play an important role in enzyme catalysis. A protein without its prosthetic group is called an apoprotein, while a protein combined with its prosthetic group is called a holoprotein. A non-covalently bound prosthetic group cannot generally be removed from the holoprotein without denaturating the protein.
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This usually uses a prosthetic group or a coenzyme, forming electrophilic alpha and beta unsaturated carbonyl compounds and imines.
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FMN Flavin mononucleotide is a prosthetic group found in, among other proteins, NADH dehydrogenase, E.coli nitroreductase and old yellow enzyme.
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Binding of oxygen to a heme prosthetic group, which would be part of a hemoprotein. A hemeprotein (or haemprotein; also hemoprotein or haemoprotein), or heme protein, is a protein that contains a heme prosthetic group. They are very large class of metalloproteins. The heme group confers functionality, which can include oxygen carrying, oxygen reduction, electron transfer, and other processes.
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Structures of the three main molecules involved in chemical reaction catalyzed by the tyrosine aminotransferase enzyme are shown below: the amino acid tyrosine, the prosthetic group pyridoxal phosphate, and the resulting product 4-hydroxyphenylpyruvate. Image:3strucfinal.jpg dimer. The prosthetic group PLP is visible in both monomers. Each side of the dimer protein includes pyridoxal phosphate (PLP) bonded to the Lys280 residue of the tyrosine aminotransferase molecule.
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The enzyme formylmethanofuran:tetrahydromethanopterin formyltransferase catalyzes the transfer of the formyl group from formylmethanofuran to N5 on tetrahydromethanopterin, . This enzyme has been crystallized; it contains no prosthetic group.
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Coelenterazine Coelenterazine is found in radiolarians, ctenophores, cnidarians, squid, brittle stars, copepods, chaetognaths, fish, and shrimp. It is the prosthetic group in the protein aequorin responsible for the blue light emission.
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Flavoproteins have either an FMN or FAD molecule as a prosthetic group, this prosthetic group can be tightly bound or covalently linked. Only about 5-10% of flavoproteins have a covalently linked FAD, but these enzymes have stronger redox power. In some instances, FAD can provide structural support for active sites or provide stabilization of intermediates during catalysis. Based on the available structural data, the known FAD- binding sites can be divided into more than 200 types.
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The electrons enter complex I via a prosthetic group attached to the complex, flavin mononucleotide (FMN). The addition of electrons to FMN converts it to its reduced form, FMNH2. The electrons are then transferred through a series of iron–sulfur clusters: the second kind of prosthetic group present in the complex. There are both [2Fe–2S] and [4Fe–4S] iron–sulfur clusters in complex I. As the electrons pass through this complex, four protons are pumped from the matrix into the intermembrane space.
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Also, often the hydrophobic properties matter. Thereby, NSAIs activity is mostly dependent on the size and shape of the drug structure along with steric characteristics and interaction of the azole group to the heme prosthetic group .
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Phosphopantetheine, also known as 4'-Phosphopantetheine, is an essential prosthetic group of acyl carrier protein (ACP) and peptidyl carrier proteins (PCP) and aryl carrier proteins (ArCP) derived from Coenzyme A. It is also present in formyltetrahydrofolate dehydrogenase.
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Interacts with the cofactor or prosthetic group, FAD of flavoproteins and contains a flavin moiety in the form of FAD or FMN (flavin mononucleotide). The domain non-covalently binds oxidized FAD or its reduced form, hydroquinone (FADH2).
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The GCSH is a heat-stable small protein with a covalently attached lipoic acid prosthetic group which interacts with the three enzymes during the catalysis. The chemically determined amino acid sequence revealed that chicken H-protein is composed of 125 amino acids with a lipoic acid prosthetic group at lysine 59 (Lys59). Because of its restricted tissue expression in humans, H-protein purified from chicken liver has been routinely used for the assay. The H-protein comprises a mitochondrial targeting sequence and a mature mitochondrial matrix protein sequence.
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A prosthetic group is the non-amino acid component that is part of the structure of the heteroproteins or conjugated proteins, being covalently linked to the apoprotein. Not to be confused with the cofactor that binds to the enzyme apoenzyme (either a holoprotein or heteroprotein) by non-covalent binding.s a non-protein (non-amino acid) This is a component of a conjugated protein that is required for the protein's biological activity. The prosthetic group may be organic (such as a vitamin, sugar, RNA, phosphate or lipid) or inorganic (such as a metal ion).
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Sirohydrochlorin was first isolated in the early 1970s when it was shown to be the metal-free form of the prosthetic group in the ferredoxin-nitrite reductase from spinach. Its chemical identity was established by spectroscopy and by total synthesis.
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Its activation in vivo requires the attachment of a lipoic acid prosthetic group at Lys59 of the mature protein. The matrix protein sequence is highly conserved and chicken H-protein has 85.6% amino acid sequence similarity to the human form.
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Finally, the active site contains a heme prosthetic group in which the iron is tethered to a thiolate ligand on a conserved cysteine residue. This group also binds diatomic oxygen at the sixth coordination site, which is eventually incorporated onto the substrate.
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FADH and FADH2 are reduced forms of FAD. FADH2 is produced as a prosthetic group in succinate dehydrogenase, an enzyme involved in the citric acid cycle. In oxidative phosphorylation, two molecules of FADH2 typically yield 1.5 ATP each, or three ATP combined.
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Sirohydrochlorin is a tetrapyrrole macrocyclic metabolic intermediate in the biosynthesis of sirohaem, the iron-containing prosthetic group in sulfite reductase enzymes. It is also the biosynthetic precursor to cofactor F430, an enzyme which catalyzes the release of methane in the final step of methanogenesis.
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The substrate- binding site of the enzyme was determined to be at the base of a long funnel that extends 25 Å from the surface into the interior of the protein. It has also been determined that the FAD prosthetic group becomes deeply entrenched in the enzyme structure, which allows for pervasive interactions with both neighboring atoms and conserved water molecules. Additionally, this flavin- containing prosthetic group has been classified as providing snake venom with its quintessential dark yellow coloration, which is shown in Figure 2. One unusual characteristic reported for sv-LAAOs regards the cold inactivation and heat reactivation properties of the protein.
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Pathway for the biosynthesis of trans-cinnamaldehyde. The biosynthesis of cinnamaldehyde begins with deamination of L-phenylalanine into cinnamic acid by the action of phenylalanine ammonia lyase (PAL). PAL catalyzes this reaction by a non-oxidative deamination. This deamination relies on the MIO prosthetic group of PAL.
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Myoglobin and hemoglobin are globular proteins that serve to bind and deliver oxygen using a prosthetic group. These globins dramatically improve the concentration of molecular oxygen that can be carried in the biological fluids of vertebrates and some invertebrates. Differences occur in ligand binding and allosteric regulation.
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Assembly of the hydrophobic anchor consisting of subunits SDHC and SDHD remains unclear. Especially in case of heme b insertion and even its function. Heme b prosthetic group does not appear to be part of electron transporting pathway within the complex II. The cofactor rather maintains the anchor stability.
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The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members include myoglobin and hemoglobin. Both of these proteins reversibly bind oxygen via a heme prosthetic group.
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Close-up rendering of active site of human carbonic anhydrase II, showing three histidine residues and a hydroxide group coordinating (dashed lines) the zinc ion at center. From . A zinc prosthetic group in the enzyme is coordinated in three positions by histidine side-chains. The fourth coordination position is occupied by water.
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Hemoglobin (Hb) is the primary vehicle for transporting oxygen in the blood. Each hemoglobin molecule has the capacity to carry four oxygen molecules. These molecules of oxygen bind to the iron of the heme prosthetic group. When hemoglobin has no bound oxygen, nor bound carbon dioxide, it has the unbound conformation (shape).
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Aequorin is also a useful tool to indicate calcium level inside cells; however, it has some limitations, primarily is that its prosthetic group coelenterazine is consumed irreversibly when emits light, thus requires continuous addition of coelenterazine into the media. To overcome such issues, Tsien's group also developed the calmodulin- based sensor, named Cameleon.
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Dihydrosirohydrochlorin is one of several naturally occurring tetrapyrrole macrocyclic metabolic intermediates in the biosynthesis of vitamin B12 (cobalamin). Its oxidised form, sirohydrochlorin, is precursor to sirohaem, the iron-containing prosthetic group in sulfite reductase enzymes. Further biosynthetic transformations convert sirohydrochlorin to cofactor F430 for an enzyme which catalyzes the release of methane in the final step of methanogenesis.
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The primary limitation of aequorin is that the prosthetic group coelenterazine is irreversibly consumed to produce light, and requires continuous addition of coelenterazine into the media. Such issues led to developments of other genetically encoded calcium sensors including the calmodulin-based sensor cameleon, developed by Roger Tsien and the troponin- based sensor, TN-XXL, developed by Oliver Griesbeck.
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This process facilitates the production of fatty acids in cells, which are essential in cell membrane structure. Coenzyme A is also the source of the phosphopantetheine group that is added as a prosthetic group to proteins such as acyl carrier protein and formyltetrahydrofolate dehydrogenase.Some of the sources that CoA comes from and uses in the cell.
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Very-long-chain acyl-CoA dehydrogenase (, ACADVL (gene).) is an enzyme with systematic name very-long-chain acyl-CoA:electron-transfer flavoprotein 2,3-oxidoreductase. This enzyme catalyses the following chemical reaction : a very-long-chain acyl-CoA + electron-transfer flavoprotein \rightleftharpoons a very-long-chain trans-2,3-dehydroacyl-CoA + reduced electron-transfer flavoprotein This enzyme contains FAD as prosthetic group.
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Soluble quinoprotein glucose dehydrogenase (, soluble glucose dehydrogenase, sGDH, glucose dehydrogenase (PQQ-dependent)) is an enzyme with systematic name D-glucose:acceptor oxidoreductase. This enzyme catalyses the following chemical reaction : D-glucose + acceptor \rightleftharpoons D-glucono-1,5-lactone + reduced acceptor This soluble periplasmic enzyme contains PQQ as prosthetic group, and is bound to a calcium ion. Electron acceptor is not known.
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This is the case for the sugar and lipid moieties in glycoproteins and lipoproteins or RNA in ribosomes. They can be very large, representing the major part of the protein in proteoglycans for instance. The heme group in hemoglobin is a prosthetic group. Further examples of organic prosthetic groups are vitamin derivatives: thiamine pyrophosphate, pyridoxal- phosphate and biotin.
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The resulting carbanion is stabilized by the structure of the carbanion itself via resonance charge distribution and by the presence of a charged ion prosthetic group. Triosephosphate isomerase rapidly interconverts dihydroxyacetone phosphate with glyceraldehyde 3-phosphate (GADP) that proceeds further into glycolysis. This is advantageous, as it directs dihydroxyacetone phosphate down the same pathway as glyceraldehyde 3-phosphate, simplifying regulation.
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Structure of siroheme Siroheme (or sirohaem) is a heme-like prosthetic group at the active sites of some enzymes to accomplish the six-electron reduction of sulfur and nitrogen. It is a cofactor at the active site of sulfite reductase, which plays a major role in sulfur assimilation pathway, converting sulfite into sulfide, which can be incorporated into the organic compound homocysteine.
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Thioredoxin reductases (TR, TrxR) () are the only known enzymes to reduce thioredoxin (Trx). Two classes of thioredoxin reductase have been identified: one class in bacteria and some eukaryotes and one in animals. Both classes are flavoproteins which function as homodimers. Each monomer contains a FAD prosthetic group, a NADPH binding domain, and an active site containing a redox-active disulfide bond.
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The next step is priming, or the initiation of fatty acid synthesis. Priming is performed in the β subunit, and is catalyzed by the acetyltransferase (AT) domain, which initiates the process of fatty acid synthesis. Here, acetyltransferase transfers the acetate group from acetyl-CoA onto the SH group of the 4′-phosphopantetheine prosthetic group of ACP, which had been attached during activation.
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Although MIO is a polypeptide modification, it was proposed to call it a prosthetic group, because it has the quality of an added organic compound. PAL is inhibited by trans-cinnamic acid, and, in some species, may be inhibited by trans-cinnamic acid derivatives. The unnatural amino acids D-Phe and D-Tyr, the enantiomeric forms of the normal substrate, are competitive inhibitors.
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Hemoglobin and myoglobin are examples of hemeproteins that respectively transport and store of oxygen in mammals. Hemoglobin is a quaternary protein that occurs in the red blood cell, whereas, myoglobin is a tertiary protein found the muscle cells of mammals. Although they might differ in location and size, their function are similar. Being hemeproteins, they both contain a heme prosthetic group.
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Octaethylporphyrin (H2OEP) is an organic compound that is a relative of naturally occurring heme pigments. The compound is used in the preparation of models for the prosthetic group in heme proteins. It is a dark purple solid that is soluble in organic solvents. When treated with ferric chloride in hot acetic acid solution, it forms the square pyramidal complex Fe(OEP)Cl.
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Other oxygen transporting proteins have a very low dissociation constant with their metal prosthetic group and bind these groups tightly. Vanabins on the other hand have a moderate dissociation constant and do not tightly bind vanadium. Most importantly, because of this moderate dissociation constant, vanadium is usually found free-floating and separated from any proteins inside the vacuoles. This is completely different from other oxygen transporting proteins.
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The most widely observed cofactor involved in dioxygenation reactions is iron, but the catalytic scheme employed by these iron-containing enzymes is highly diverse. Iron-containing dioxygenases can be subdivided into three classes on the basis of how iron is incorporated into the active site: those employing a mononuclear iron center, those containing a Rieske [2Fe-2S] cluster, and those utilizing a heme prosthetic group.
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A chromoprotein is a conjugated protein that contains a pigmented prosthetic group (or cofactor). A common example is haemoglobin, which contains a heme cofactor, which is the iron-containing molecule that makes oxygenated blood appear red. Other examples of chromoproteins include other hemochromes, cytochromes, phytochromes and flavoproteins. In hemoglobin there exists a chromoprotein (tetramer MW:4 x 16.125 =64.500), namely heme, consisting of Fe++ four pyrrol rings.
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The human thromboxane A (TXA) synthase is a 60 kDa protein with 533 amino acids and a heme prosthetic group. This enzyme, anchored to the endoplasmic reticulum, is found in platelets, monocytes, and several other cell types. The NH2 terminus contains two hydrophobic segments whose secondary structure is believed to be helical. Evidence suggests that the peptides serve as a membrane anchor for the enzyme.
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Thus, the term "prosthetic group" is a very general one and its main emphasis is on the tight character of its binding to the apoprotein. It defines a structural property, with oppostion of the term "coenzyme" that defines a functional property. Prosthetic groups are a subset of cofactors. Loosely bound metal ions and coenzymes are still cofactors, but are generally not called prosthetic groups.
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Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin: the flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN). Flavoproteins are involved in a wide array of biological processes, including removal of radicals contributing to oxidative stress, photosynthesis, and DNA repair. The flavoproteins are some of the most-studied families of enzymes. Flavoproteins have either FMN or FAD as a prosthetic group or as a cofactor.
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Here, cofactors were defined as an additional substance apart from protein and substrate that is required for enzyme activity and a prosthetic group as a substance that undergoes its whole catalytic cycle attached to a single enzyme molecule. However, the author could not arrive at a single all-encompassing definition of a "coenzyme" and proposed that this term be dropped from use in the literature.
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This enzyme participates in methane metabolism. Prior to the discovery of this enzyme, methanol oxidation in Gram-negative bacteria had been shown to be by way of an (NAD+) independent alcohol dehydrogenase found originally in Pseudomonas M27. This enzyme (EC. 1.1.99.8) contains a prosthetic group called Pyrrolo Quinoline Quinone (PQQ) that accepts the electrons generated from methanol oxidation and passes these electrons to cytochrome c.
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The coenzyme is the C1 donor in methanogenesis. It is converted to methyl-coenzyme M thioether, the thioether , in the penultimate step to methane formation. Methyl-coenzyme M reacts with coenzyme B, 7-thioheptanoylthreoninephosphate, to give a heterodisulfide, releasing methane: : + HS–CoB -> \+ CoB–S–S–CoM This induction is catalyzed by the enzyme methyl-coenzyme M reductase, which restricts cofactor F430 as the prosthetic group.
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Appears green when deoxygenated and red when oxygenated. ;Vanabins: Also known as vanadium chromagens, they are found in the blood of sea squirts. They were once hypothesized to use the rare metal vanadium as an oxygen binding prosthetic group. However, although they do contain vanadium by preference, they apparently bind little oxygen, and thus have some other function, which has not been elucidated (sea squirts also contain some hemoglobin).
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A representation of the 3D structure of the protein myoglobin showing turquoise α-helices. This protein was the first to have its structure solved by X-ray crystallography. Toward the right-center among the coils, a prosthetic group called a heme group (shown in gray) with a bound oxygen molecule (red). Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues.
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Kynurenine 3-monooxygenase is a dimer containing asymmetric subunits and has one FAD- binding domain as its prosthetic group. Kynurenine 3-monooxygenase contains a linker region involved in substrate binding following a second strand of an antiparallel β-sheet, a six-stranded antiparallel β-sheet domain, and an α-helix at the carboxy-terminal. The hydrophobic C-terminus acts as the mitochondrial anchoring domain and participates in enzymatic activity.
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Upon binding the chromophore, the holoprotein, an apoprotein combined with its prosthetic group, becomes sensitive to light. If it absorbs red light it will change conformation to the biologically active Pfr form. The Pfr form can absorb far red light and switch back to the Pr form. The Pfr promotes and regulates photomorphogenesis in response to FR light, whereas Pr regulates de-etiolation in response to R light.
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Plasmodium falciparum hemozoin crystals under polarised light. Haemozoin is a disposal product formed from the digestion of blood by some blood-feeding parasites. These hematophagous organisms such as malaria parasites (Plasmodium spp.), Rhodnius and Schistosoma digest haemoglobin and release high quantities of free heme, which is the non-protein component of hemoglobin. Heme is a prosthetic group consisting of an iron atom contained in the center of a heterocyclic porphyrin ring.
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Many metal cations are also required in the process. EDTA control and extensive cation presence/absence tests show that Ca(II), Mn(II), Cu(II) and Zn(II) are all essential in this process, probably functioning as a part of a coenzyme or prosthetic group. Mg(II) has partial effect, while Fe(II) and Fe(III) are inhibitory to some degree. Flagella are considered to contribute to pellicle formation.
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Left: protoporphyrin IX. Right: modified form of heme cofactor released from peroxidase by protease digestion under nonreducing conditions. The active site of eosinophil peroxidase contains a single iron atom in tetradentate complexation with a protoporphyrin IX cofactor. It is notable in that this prosthetic group is linked covalently to the polypeptide via ester bonds. Asp232 and Glu380 of EPO are covalently linked through their terminal oxygen atoms to the modified side chains of the protoporphyrin.
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Flavin Adenine Dinucleotide FAD, or flavin adenine dinucleotide, is a prosthetic group (a non-polypeptide unit bound to a protein that is required for function) that consists of an adenine nucleotide and a flavin mononucleotide. FAD is a unique electron acceptor. Its fully reduced form is FADH2 (known as the hydroquinone form), but FAD can also be partially oxidized as FADH by either reducing FAD or oxidizing FADH2. Dehydrogenases typically fully reduce FAD to FADH2.
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To date, a number of QFR enzymes have been crystalized and the specifics of enzyme structure varies between organisms; however, the overall structure remains similar across different species. Fumarate reductase complexes include four subunits. Subunit A contains the site of fumarate reduction and a covalently bound flavin adenine dinucleotide (FAD) prosthetic group. It is closely bound to subunit B, which contains three iron-sulfur centers, all placed near to each other and the nearby substrates.
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It was discovered by J.G. Hauge as the third redox cofactor after nicotinamide and flavin in bacteria (although he hypothesised that it was naphthoquinone). Anthony and Zatman also found the unknown redox cofactor in alcohol dehydrogenase. In 1979, Salisbury and colleagues as well as Duine and colleagues extracted this prosthetic group from methanol dehydrogenase of methylotrophs and identified its molecular structure. Adachi and colleagues discovered that PQQ was also found in Acetobacter.
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The first is called a "prosthetic group", which consists of a coenzyme that is tightly or even covalently, and permanently bound to a protein. The second type of coenzymes are called "cosubstrates", and are transiently bound to the protein. Cosubstrates may be released from a protein at some point, and then rebind later. Both prosthetic groups and cosubstrates have the same function, which is to facilitate the reaction of enzymes and protein.
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Malonyl-CoA:ACP Transacylase uses a ping-pong kinetic mechanism with a bound malony ester as the acyl intermediate attached to a serine residue residing within a GHSLG pentapeptide. FabD first binds malonyl-CoA, the malonyl moiety is then transferred to the active siteSer 92, and CoA is released from the enzyme. ACP then binds and the malonyl moiety is transferred to the terminal sulfhydryl of the ACP prosthetic group. This reaction is readily reversible.
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O2-binding induces "spin-pairing": the five-coordinate ferrous deoxy form is high spin and the six coordinate oxy form is low spin and diamagnetic. This is an image of an oxygenated myoglobin molecule. The image shows the structural change when oxygen is bound to the iron atom of the heme prosthetic group. The oxygen atoms are colored in green, the iron atom is colored in red, and the heme group is colored in blue.
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Coenzyme B is a coenzyme required for redox reactions in methanogens. The full chemical name of coenzyme B is 7-mercaptoheptanoylthreoninephosphate. The molecule contains a thiol, which is its principal site of reaction. Coenzyme B reacts with 2-methylthioethanesulfonate (methyl-Coenzyme M, abbreviated ), to release methane in methanogenesis: : + HS–CoB -> \+ CoB–S–S–CoM This conversion is catalyzed by the enzyme methyl coenzyme M reductase, which contains cofactor F430 as the prosthetic group.
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The SDHA gene is located on the p arm of chromosome 5 at locus 15 and is composed of 16 exons. The SDHA protein encoded by this gene is 664 amino acids long and weighs 72.7 kDA. SDHA protein has four subdomains, including capping domain, helical domain, C-terminal domain and most notably, β-barrel FAD-binding domain at N-terminus. Therefore, SDHA is a flavoprotein (Fp) due to the prosthetic group flavin adenine dinucleotide (FAD).
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In order to overcome these obstacles, protein or peptide labeling can be performed through a prosthetic group or bifunctional labeling agent to which the radiofluorine has been attached. This molecule can then be conjugated to the protein or peptide under milder conditions. center The three main categories of prosthetic groups are carboxyl-reactive, amino- reactive, and thiol-reactive. Of these three, the carboxyl-reactive group is the least utilized, and the amino-reactive is the most utilized.
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The activation of yeast FAS occurs in the alpha subunit. The reaction is performed by the phosphopantetheinyl transferase (PPT) domain. PPT attaches the 4′-phosphopantetheine prosthetic group of CoA to the acyl carrier protein (ACP) domain, which is found in the N terminus of the α subunit. ACP is the only “mobile” domain of the enzyme complex, in which it moves intermediate substrates along all of the catalytic centers the enzyme, most notably the alpha and beta subunits.
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Heme prosthetic group of cytochrome c, consisting of a rigid porphyrin ring coordinated with an iron atom. The cytochrome complex, or cyt c, is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins and plays a major role in cell apoptosis. Cytochrome c is highly water-soluble, unlike other cytochromes, and is an essential component of the electron transport chain, where it carries one electron.
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Structure of heme c While most heme proteins are attached to the prosthetic group through iron ion ligation and tertiary interactions, the heme group of cytochrome c makes thioether bonds with two cysteine side chains of the protein. One of the main properties of heme c, which allows cytochrome c to have variety of functions, is its ability to have different reduction potentials in nature. This property determines the kinetics and thermodynamics of an electron transfer reaction.
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Aequorin is a holoprotein composed of two distinct units, the apoprotein that is called apoaequorin, which has an approximate molecular weight of 21 kDa, and the prosthetic group coelenterazine, the luciferin. This is to say, apoaequorin is the enzyme produced in the photocytes of the animal, and coelenterazine is the substrate whose oxidation the enzyme catalyzes. When coelenterazine is bound, it is called aequorin. Notably, the protein contains three EF hand motifs that function as binding sites for Ca2+ ions.
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The flavin-containing monooxygenase (FMO) protein family specializes in the oxidation of xeno-substrates in order to facilitate the excretion of these compounds from living organisms. These enzymes can oxidize a wide array of heteroatoms, particularly soft nucleophiles, such as amines, sulfides, and phosphites. This reaction requires an oxygen, an NADPH cofactor, and an FAD prosthetic group. FMOs share several structural features, such as a NADPH binding domain, FAD binding domain, and a conserved arginine residue present in the active site.
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The chromophore is a linear tetrapyrrole called phytochromobilin. There are two forms of phytochromes: red light absorbing, Pr, and far-red light absorbing, Pfr. Pfr, which is the active form of phytochromes, can be reverted to Pr, which is the inactive form, slowly by inducing darkness or more rapidly by irradiation by far-red light. The phytochrome apoprotein, a protein that together with a prosthetic group forms a particular biochemical molecule such as a hormone or enzyme, is synthesized in the Pr form.
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Blood is rich in proteins, consisting mainly of hemoglobin (Hb), which accounts for approximately 60% of the blood protein content. The digestion of hemoglobin results in the release of high levels of the prosthetic group heme. Heme acts as a toxic molecule that can generate oxygen-reactive species and bypass membranes due to its high permeability. Elevated levels of heme in female L. longipalpis are suspected to be the cause of increased mortality for females that have ingested multiple blood meals.
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This nuclear gene, COX10, encodes heme A: farnesyltransferase, which is not a structural subunit but required for the expression of functional COX and functions in the maturation of the heme A prosthetic group of COX. A gene mutation, which results in the substitution of a lysine for an asparagine (N204K), is identified to be responsible for cytochrome c oxidase deficiency. In addition, this gene is disrupted in patients with CMT1A (Charcot-Marie-Tooth type 1A) duplication and with HNPP (hereditary neuropathy with liability to pressure palsies) deletion.
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The level of methylmalonic acid is not elevated in folic acid deficiency. Direct measurement of blood cobalamin remains the gold standard because the test for elevated methylmalonic acid is not specific enough. Vitamin B is one necessary prosthetic group to the enzyme methylmalonyl-coenzyme A mutase. Vitamin B deficiency is but one among the conditions that can lead to dysfunction of this enzyme and a buildup of its substrate, methylmalonic acid, the elevated level of which can be detected in the urine and blood.
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Cofactors can be divided into two major groups: organic cofactors, such as flavin or heme; and inorganic cofactors, such as the metal ions Mg2+, Cu+, Mn2+ and iron-sulfur clusters. Organic cofactors are sometimes further divided into coenzymes and prosthetic groups. The term coenzyme refers specifically to enzymes and, as such, to the functional properties of a protein. On the other hand, "prosthetic group" emphasizes the nature of the binding of a cofactor to a protein (tight or covalent) and, thus, refers to a structural property.
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The crystal structure of NADH peroxidase resembles glutathione reductase with respect to chain fold and location as well as conformation of the prosthetic group FAD His10 of the NADH peroxidase is located near the N-terminus of the R1 helix within the FAD-binding site. One of the oxygen atoms of Cys42-SO3H is hydrogen-bonded both to the His10 imidazole and to Cys42 N terminus. The His10 functions in part to stabilize the unusual Cys42-SOH redox center. Arg303 also stabilizes the Cys42-SO3H.
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Each module uses one molecule of the selected substrate amino acid with one molecule of ATP to give an aminoacyl adenylate enzyme complex and pyrophosphate. The activated amino acid can then be transferred to the enzyme bound 4'-phosphopantetheine of the carrier protein with the expulsion of AMP from the system. The carrier protein uses the 4'-phosphopantetheine prosthetic group for loading of the growing peptide and their monomer precursors. Elongation of the peptide chain is achieved through condensation of the upstream PCP onto an adjacent downstream PCP-bound monomer.
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Organic cofactors are small organic molecules (typically a molecular mass less than 1000 Da) that can be either loosely or tightly bound to the enzyme and directly participate in the reaction. In the latter case, when it is difficult to remove without denaturing the enzyme, it can be called a prosthetic group. It is important to emphasize that there is no sharp division between loosely and tightly bound cofactors. Indeed, many such as NAD+ can be tightly bound in some enzymes, while it is loosely bound in others.
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The fatty acids are synthesized by a series of decarboxylative Claisen condensation reactions from acetyl-CoA and malonyl-CoA. Following each round of elongation the beta keto group is reduced to the fully saturated carbon chain by the sequential action of a ketoreductase (KR), dehydratase (DH), and enoyl reductase (ER). The growing fatty acid chain is carried between these active sites while attached covalently to the phosphopantetheine prosthetic group of an acyl carrier protein (ACP), and is released by the action of a thioesterase (TE) upon reaching a carbon chain length of 16 (palmitic acid).
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Early studies of the bioluminescence of Aequorea by E. Newton Harvey had noted that the bioluminescence appears as a ring around the bell, and occurs even in the absence of air. This was remarkable because most bioluminescence reactions appeared to require oxygen, and led to the idea that the animals somehow store oxygen. It was later discovered that the apoprotein can stably bind coelenterazine and oxygen is required for the regeneration to the active form of aequorin. However, in the presence of calcium ions, the protein undergoes a conformational change and through oxidation converts its prosthetic group, coelenterazine, into excited coelenteramide and CO2.
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Recently, FMO enzymes have received a great deal of attention from the pharmaceutical industry both as a drug target for various diseases and as a means to metabolize pro-drug compounds into active pharmaceuticals. These monooxygenases are often misclassified because they share activity profiles similar to those of cytochrome P450 (CYP450), which is the major contributor to oxidative xenobiotic metabolism. However, a key difference between the two enzymes lies in how they proceed to oxidize their respective substrates; CYP enzymes make use of an oxygenated heme prosthetic group, while the FMO family utilizes FAD to oxidize its substrates.
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Short-chain acyl-CoA dehydrogenase (, butyryl-CoA dehydrogenase, butanoyl-CoA dehydrogenase, butyryl dehydrogenase, unsaturated acyl-CoA reductase, ethylene reductase, enoyl-coenzyme A reductase, unsaturated acyl coenzyme A reductase, butyryl coenzyme A dehydrogenase, short-chain acyl CoA dehydrogenase, short- chain acyl-coenzyme A dehydrogenase, 3-hydroxyacyl CoA reductase, butanoyl- CoA:(acceptor) 2,3-oxidoreductase, ACADS (gene).) is an enzyme with systematic name short-chain acyl-CoA:electron-transfer flavoprotein 2,3-oxidoreductase. This enzyme catalyses the following chemical reaction : a short-chain acyl-CoA + electron-transfer flavoprotein \rightleftharpoons a short-chain trans-2,3-dehydroacyl-CoA + reduced electron-transfer flavoprotein This enzyme contains FAD as prosthetic group.
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Medium-chain acyl-CoA dehydrogenase (, fatty acyl coenzyme A dehydrogenase (ambiguous), acyl coenzyme A dehydrogenase (ambiguous), acyl dehydrogenase (ambiguous), fatty-acyl-CoA dehydrogenase (ambiguous), acyl CoA dehydrogenase (ambiguous), general acyl CoA dehydrogenase (ambiguous), medium-chain acyl- coenzyme A dehydrogenase, acyl-CoA:(acceptor) 2,3-oxidoreductase (ambiguous), ACADM (gene name).) is an enzyme with systematic name medium-chain acyl- CoA:electron-transfer flavoprotein 2,3-oxidoreductase. This enzyme catalyses the following chemical reaction : a medium-chain acyl-CoA + electron-transfer flavoprotein \rightleftharpoons a medium-chain trans-2,3-dehydroacyl-CoA + reduced electron-transfer flavoprotein This enzyme contains FAD as prosthetic group.
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Long-chain acyl-CoA dehydrogenase (, palmitoyl-CoA dehydrogenase, palmitoyl- coenzyme A dehydrogenase, long-chain acyl-coenzyme A dehydrogenase, long- chain-acyl-CoA:(acceptor) 2,3-oxidoreductase, ACADL (gene).) is an enzyme with systematic name long-chain acyl-CoA:electron-transfer flavoprotein 2,3-oxidoreductase. This enzyme catalyses the following chemical reaction : a long-chain acyl-CoA + electron-transfer flavoprotein \rightleftharpoons a long-chain trans-2,3-dehydroacyl-CoA + reduced electron-transfer flavoprotein This enzyme contains FAD as prosthetic group and participates in fatty acid metabolism and PPAR signaling pathway. Mitochondrial mutations in this enzyme may be associated with some forms of dilated cardiomyopathy.
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It was originally believed that due to light emissions resembling that of retinal bound rhodopsin, the photosensor molecule bound to PYP should resemble the structure of retinal bound rhodopsin, the photosensor molecule bound to PYP should resemble the structure of retinal. Scientists were therefore amazed when the PYP Cys 69 was bound by a thiol ester linkage as the light sensitive prosthetic group p-coumaric acid. During the photoreactive mechanism: # Light absorption yields the native protein to absorb a maximum wavelength of 446 nm, ε = 45500 M−1 cm−1. # Within a nanosecond the absorbed maximum wavelength is shifted to 465 nm.
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NAD+ to NADH The enzymatic oxidoreduction reaction catalyzed by NDH-2 may be described as follows: NADH + Q + H+ \-----> NAD+ \+ QH2 (Q - quinone; QH2 \- quinol) In this case, the electron donor is NADH and the electron acceptor is the quinone. Depending on the organism, the reduced quinone changes between menaquinone, ubiquinone or plastoquinone. The mechanism of the reaction may be divided in two half-reactions: 1stHR and 2ndHR. In the 1stHR, 2 electrons and 1 proton from NADH are transferred (simultaneously with an additional proton from the bulk) to the prosthetic group (FAD), giving rise to its protonated form FADH2.
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The cofactor TPP, C12 H18 N4 O7 P2 S, is needed for this reaction's mechanism; it acts as the prosthetic group to the enzyme. The carbon atom between the sulfur and nitrogen atoms on thiazole ring act as carbanion which binds to the pyruvate. TPP has an acidic H+ on its C2 that acts as the functional part of the thiazolium ring; the ring acts as an "electron sink", enabling the carbanion electrons to be stabilized by resonance. The TPP can then act as a nucleophile with the loss of this C2 hydrogen, forming the ylide form of TPP.
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Glutathione reductase (GR) also known as glutathione-disulfide reductase (GSR) is an enzyme that in humans is encoded by the GSR gene. Glutathione reductase (EC 1.8.1.7) catalyzes the reduction of glutathione disulfide (GSSG) to the sulfhydryl form glutathione (GSH), which is a critical molecule in resisting oxidative stress and maintaining the reducing environment of the cell. Glutathione reductase functions as dimeric disulfide oxidoreductase and utilizes an FAD prosthetic group and NADPH to reduce one molar equivalent of GSSG to two molar equivalents of GSH: General reaction catalyzed by glutathione reductase The glutathione reductase is conserved between all kingdoms.
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The flavin moiety is often attached with an adenosine diphosphate to form flavin adenine dinucleotide (FAD), and, in other circumstances, is found as flavin mononucleotide (or FMN), a phosphorylated form of riboflavin. It is in one or the other of these forms that flavin is present as a prosthetic group in flavoproteins. The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two-step process or two electrons at once. Reduction is made with the addition of hydrogen atoms to specific nitrogen atoms on the isoalloxazine ring system: Equilibrium between the oxidized (left) and totally reduced (right) forms of flavin.
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While no scientific literature reports a crystal image of a kynurenine 3-monooxygenase complex with -kynurenine, structural studies of the enzyme in yeast co-crystallized with UPF 648 reveal how the FAD cofactor and substrate are bound in the active site. Chemical similarities between UPF 648 and -kynurenine suggest that the substrate binds adjacent to the Re-face of the flavoprotein. A loop containing the residues Pro321–Gln325 is believed to be the oxygen-binding site above the re-side of the FAD prosthetic group. Each monomer contains a conserved hydrophobic pocket (residues Leu221, Met230, Ile232, Leu234, Phe246, Pro321, Phe322) positioned around the substrate’s aromatic benzene moiety.
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All redox reactions take place in the hydrophilic domain of complex I. NADH initially binds to complex I, and transfers two electrons to the flavin mononucleotide (FMN) prosthetic group of the enzyme, creating FMNH2. The electron acceptor – the isoalloxazine ring – of FMN is identical to that of FAD. The electrons are then transferred through the FMN via a series of iron-sulfur (Fe-S) clusters, and finally to coenzyme Q10 (ubiquinone). This electron flow changes the redox state of the protein, inducing conformational changes of the protein which alters the pK values of ionizable side chain, and causes four hydrogen ions to be pumped out of the mitochondrial matrix.
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Metmyoglobin is the oxidised form of the oxygen-carrying hemeprotein myoglobin. Metmyoglobin is the cause of the characteristic brown colouration of meat that occurs as it ages. In living muscle, the concentration of metmyoglobin is vanishingly small, due to the presence of the enzyme metmyoglobin reductase, which, in the presence of the cofactor NADH and the coenzyme cytochrome b4 converts the Fe3+ in the heme prosthetic group of metmyoglobin back to the Fe2+ of normal myoglobin. In meat, which is dead muscle, the normal processes of removing metmyoglobin are prevented from effecting this repair, or alternatively the rate of metmyoglobin formation exceeds their capacity, so that there is a net accumulation of metmyoglobin as the meat ages.
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It was originally thought that the heme prosthetic group for plant leghemoglobin was provided by the bacterial symbiont within symbiotic root nodules. However, subsequent work shows that the plant host strongly expresses heme biosynthesis genes within nodules, and that activation of those genes correlates with leghemoglobin gene expression in developing nodules. In plants colonised by Rhizobium, such as alfalfa or soybeans, the presence of oxygen in the root nodules would reduce the activity of the oxygen-sensitive nitrogenase, which is an enzyme responsible for the fixation of atmospheric nitrogen. Leghemoglobin is shown to buffer the concentration of free oxygen in the cytoplasm of infected plant cells to ensure the proper function of root nodules.
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In the general porphyrin biosynthesis pathway, uroporphyrinogen III is derived from the linear tetrapyrrole preuroporphyrinogen (a substituted hydroxymethylbilane) by the action of the enzyme uroporphyrinogen-III cosynthase. alt=Biosynthesis of Uroporphyrinogen-III from pre-uroporphyrinogen The conversion entails a reversal of the last pyrrole unit (thus swapping the acetic and propionic acid groups) and a condensation reaction that closes the macrocycle by eliminating the final hydroxyl with a hydrogen atom of the first ring. In the biosynthesis of hemes and chlorophylls, uroporphyrinogen III is converted into coproporphyrinogen III by the enzyme uroporphyrinogen III decarboxylase. In the biosynthesis of sirohemes, uroporphyrinogen III is converted by two methyl transferases to dihydrosirohydrochlorin, which is subsequently oxidized sirohydrochlorin, a precursor to the siroheme prosthetic group.
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The positive charges of the ions that enter the cell down its electrochemical gradient change the cell's membrane potential, cause depolarization, and lead to the release of the neurotransmitter glutamate. Glutamate can depolarize some neurons and hyperpolarize others, allowing photoreceptors to interact in an antagonistic manner. When light hits photoreceptive pigments within the photoreceptor cell, the pigment changes shape. The pigment, called rhodopsin (conopsin is found in cone cells) comprises a large protein called opsin (situated in the plasma membrane), attached to which is a covalently bound prosthetic group: an organic molecule called retinal (a derivative of vitamin A). The retinal exists in the 11-cis-retinal form when in the dark, and stimulation by light causes its structure to change to all-trans-retinal.
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The oxygenase domain is a unique extended beta sheet cage with binding sites for heme and pterin. NOSs can be dimeric, calmodulin-dependent or calmodulin-containing cytochrome p450-like hemoprotein that combines reductase and oxygenase catalytic domains in one dimer, bear both flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), and carry out a 5`-electron oxidation of non-aromatic amino acid arginine with the aid of tetrahydrobiopterin. All three isoforms (each of which is presumed to function as a homodimer during activation) share a carboxyl-terminal reductase domain homologous to the cytochrome P450 reductase. They also share an amino- terminal oxygenase domain containing a heme prosthetic group, which is linked in the middle of the protein to a calmodulin-binding domain.
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Binding of calmodulin appears to act as a "molecular switch" to enable electron flow from flavin prosthetic groups in the reductase domain to heme. This facilitates the conversion of O2 and L-arginine to NO and L-citrulline. The oxygenase domain of each NOS isoform also contains an BH4 prosthetic group, which is required for the efficient generation of NO. Unlike other enzymes where BH4 is used as a source of reducing equivalents and is recycled by dihydrobiopterin reductase (), BH4 activates heme-bound O2 by donating a single electron, which is then recaptured to enable nitric oxide release. The first nitric oxide synthase to be identified was found in neuronal tissue (NOS1 or nNOS); the endothelial NOS (eNOS or NOS3) was the third to be identified.
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In the detailed reaction mechanism, the hydronium atoms that are added in come from a variety of residues that offer hydrogen bonds to facilitate ALA synthesis. ALA synthase removes the carboxyl group from glycine and the CoA from the succinyl-CoA by means of its prosthetic group pyridoxal phosphate (a vitamin b6 derivative), forming δ-aminolevulinic acid (dALA), so called because the amino group is on the fourth carbon atom in the molecule. This reaction mechanism is particularly unique relative to other enzymes that use the PLP cofactor because Glycine is initially deprotonated by a highly conserved active site lysine, leading to condensation with succinyl-CoA and loss of CoA. Protonation of the carbonyl group of the intermediate by an active site histidine leads to loss of the carboxyl group.
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The pigment, called iodopsin or rhodopsin, consists of large proteins called opsin (situated in the plasma membrane), attached to a covalently bound prosthetic group: an organic molecule called retinal (a derivative of vitamin A). The retinal exists in the 11-cis-retinal form when in the dark, and stimulation by light causes its structure to change to all-trans-retinal. This structural change causes opsin (a G protein-coupled receptor) to activate its G protein transducin, which leads to the activation of cGMP phosphodiesterase, which breaks cGMP down into 5'-GMP. Reduction in cGMP allows the ion channels to close, preventing the influx of positive ions, hyperpolarizing the cell, and stopping the release of neurotransmitters. The entire process by which light initiates a sensory response is called visual phototransduction.
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COX15 is one of the cytochrome c oxidase (COX) assembly factors identified in yeast, playing a key role in the biosynthetic pathway of mitochondrial heme A, the prosthetic group of cytochrome a and a3. COX15 in yeast mediates hydroxylation of the methyl group at the C-8 position of the heme O molecule to form heme A. A deletion of COX15 results in undetectable levels of heme A but detectable levels of heme O. Similar findings are observed in patients with COX15 deletion mutants, suggesting a similar functional role for COX15 in mammalian mitochondria and a similar pathogenesis for the COX deficiency. In complex IV of the respiratory chain, heme A is required for the proper folding of the Cox 1 subunit and subsequent assembly. A deficiency in the formation of heme A and functional COX would lead to impaired electron transport and oxidative phosphorylation.
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While most iron-dependent dioxygenases utilize a non-heme iron cofactor, the oxidation of L-(and D-)tryptophan to N-formylkynurenine is catalyzed by either tryptophan 2,3-dioxygenase (TDO) or indoleamine 2,3-dioxygenase (IDO), which are heme dioxygenases that utilize iron coordinated by a heme B prosthetic group. While these dioxygenases are of interest in part because they uniquely use heme for catalysis, they are also of interest due to their importance in tryptophan regulation in the cell, which has numerous physiological implications. The initial association of the substrate with the dioxygen-iron in the enzyme active site is thought to either proceed via radical or electrophilic addition, requiring either ferrous iron or ferric iron, respectively. While the exact reaction mechanism for the heme-dependent dioxygenases is still under debate, it is postulated that the reaction proceeds through either a dioxetane or Criegee mechanism (figures 4, 5).
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The acyl carrier protein (ACP) is an important component in both fatty acid and polyketide biosynthesis with the growing chain bound during synthesis as a thiol ester at the distal thiol of a 4'-phosphopantetheine moiety. The ACPs are related in structure and mechanism to the peptidyl carrier proteins (PCP) from nonribosomal peptide synthases. The protein is expressed in the inactive apo form and the 4'-phosphopantetheine moiety must be post-translationally attached to a conserved serine residue on the ACP by the action of holo-acyl carrier protein synthase (ACPS), a 4'-phosphopantetheinyl transferase. 4'-Phosphopantetheine is an essential prosthetic group of several acyl carrier proteins involved in pathways of primary and secondary metabolism including the acyl carrier proteins (ACP) of fatty acid synthases, ACPs of polyketide synthases, and peptidyl carrier proteins (PCP) and aryl carrier proteins (ArCP) of nonribosomal peptide synthetases (NRPS).
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An inactive enzyme without the cofactor is called an apoenzyme, while the complete enzyme with cofactor is called a holoenzyme. (Note that the International Union of Pure and Applied Chemistry (IUPAC) defines "coenzyme" a little differently, namely as a low-molecular-weight, non-protein organic compound that is loosely attached, participating in enzymatic reactions as a dissociable carrier of chemical groups or electrons; a prosthetic group is defined as a tightly bound, nonpolypeptide unit in a protein that is regenerated in each enzymatic turnover.) Some enzymes or enzyme complexes require several cofactors. For example, the multienzyme complex pyruvate dehydrogenase at the junction of glycolysis and the citric acid cycle requires five organic cofactors and one metal ion: loosely bound thiamine pyrophosphate (TPP), covalently bound lipoamide and flavin adenine dinucleotide (FAD), cosubstrates nicotinamide adenine dinucleotide (NAD+) and coenzyme A (CoA), and a metal ion (Mg2+). Organic cofactors are often vitamins or made from vitamins.
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Mammalian FAS consists of a homodimer of two identical protein subunits, in which three catalytic domains in the N-terminal section (-ketoacyl synthase (KS), malonyl/acetyltransferase (MAT), and dehydrase (DH)), are separated by a core region of 600 residues from four C-terminal domains (enoyl reductase (ER), -ketoacyl reductase (KR), acyl carrier protein (ACP) and thioesterase (TE)). The conventional model for organization of FAS (see the 'head-to-tail' model on the right) is largely based on the observations that the bifunctional reagent 1,3-dibromopropanone (DBP) is able to crosslink the active site cysteine thiol of the KS domain in one FAS monomer with the phosphopantetheine prosthetic group of the ACP domain in the other monomer. Complementation analysis of FAS dimers carrying different mutations on each monomer has established that the KS and MAT domains can cooperate with the ACP of either monomer. and a reinvestigation of the DBP crosslinking experiments revealed that the KS active site Cys161 thiol could be crosslinked to the ACP 4'-phosphopantetheine thiol of either monomer.
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