Study of carbon and nitrogen fractionations suggests a largely meat-based diet.
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Mass-independent isotope fractionation or Non-mass-dependent fractionation (NMD), refers to any chemical or physical process that acts to separate isotopes, where the amount of separation does not scale in proportion with the difference in the masses of the isotopes. Most isotopic fractionations (including typical kinetic fractionations and equilibrium fractionations) are caused by the effects of the mass of an isotope on atomic or molecular velocities, diffusivities or bond strengths. Mass-independent fractionation processes are less common, occurring mainly in photochemical and spin- forbidden reactions. Observation of mass-independently fractionated materials can therefore be used to trace these types of reactions in nature and in laboratory experiments.
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Isotopic mass balance calculations have implied that sulfate reduction and anaerobic oxidation of methane can fractionate sulfur. During sulfate reductions, the extent of sulfur fractionation varies depending on the environment and rates of reduction. Slower reduction rates lead to higher fractionations and sulfate concentration below 1 mM lead to lower fractionations. The production and consumption of methane leads to archaeal and bacterial highly depleted in 13C biomarkers, specifically lipids.
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The chondritic reservoir exhibits fractionations of 0.069 ± 0.010‰ per atomic mass unit. Isotopic variations observed on planetary bodies can help to constrain and better understand their formation and processes occurring in the early Solar System.
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Improvements in the understanding the iron isotope fractionations observed in biology will enable the development of a more complete knowledge of the enzymatic, metabolic, and other biologic pathways in different organisms. Below, the known iron isotopic variations for different classes of organisms are described.
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This meteorite is intermediate between L and LL ordinary chondrites, possibly indicating formation on a separate parent body.Kallemeyn G. W., Rubin A. E., Wang D., and Wasson J. T. Ordinary chondrites: Bulk compositions, classification, lithophile-element fractionations, and composition-petrographic type relationships. 1989, Geochim. Cosmochim. Acta, 53, 2747–2767.
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It focuses on position-specific isotope fractionations in many contexts, development of technologies to measure these fractionations and the application of position-specific isotope enrichments to questions surrounding biogeochemistry, microbiology, enzymology, medicinal chemistry, and earth history. Position-specific isotope enrichments can retain critical information about synthesis and source of the atoms in the molecule. Indeed, bulk isotope analysis averages site-specific isotope effects across the molecule, and so while all those values have an influence on the bulk value, signatures of specific processes may be diluted or indistinguishable. While the theory of position-specific isotope analysis has existed for decades, new technologies exist now to allow these methods to be much more common.
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Another example of distinct site-specific fractionations in abiotic molecules is Fischer-Tropsch-type synthesis, which is thought to produce abiogenic hydrocarbon chains. Through this reaction mechanism, site enrichments of carbon would deplete as carbon chain length increases, and be distinct from site-specific enrichments of hydrocarbons of biological origins.
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Variations in iron isotopic composition have been observed in meteorite samples from other planetary bodies. The Moon has variations in iron isotopes of 0.4‰ per atomic mass unit. Mars has very small isotope fractionation of 0.001 ± 0.006‰ per atomic mass unit. Vesta has iron fractionations of 0.010 ± 0.010‰ per atomic mass unit.
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Kinetic isotope effects are common in biological systems and are especially important for hydrogen isotope biogeochemistry. Kinetic effects usually result in larger fractionations than equilibrium reactions. In any isotope system, kinetic effects are stronger for larger mass differences. Light isotopes in most systems also tend to move faster but form weaker bonds.
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The ubication of cIAP1 is diverse depending on the phase of the living cycle of the cell. In healthy cells the protein is usually found in the nucleus. This was experimentally determined by immunofluorescence microscopy and subcellular fractionations methods. However, when the cell is apoptotic nuclear export of cIAP1 is induced provoking an increase in the cytosolic concentration of the protein.
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In sediments, oceans, and rivers, distinct trace metal isotope ratios exist due to biological processes such as metal ion uptake and abiotic processes such as adsorption to particulate matter that preferentially remove certain isotopes. The trace metal isotopic composition of a given organism results from a combination of the isotopic compositions of source material (i.e., food and water) and any fractionations imparted during metal ion uptake, translocation and processing inside cells.
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These differences in abundances are called "fractionations," which are characterized via stable isotope analysis.Dilution effect of site-specific enrichments. The 13C enrichment at the carboxylic acid site of an amino acid is less important as the structural resolution of the measurement is decreased to molecular average and bulk cell analyses. Isotope abundances can vary across an entire substrate (i.e., “bulk” isotope variation), specific compounds within a substrate (i.e.
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Vapor isotope effects occur for protium, deuterium, and tritium, because each isotope has different thermodynamic properties in the liquid and gaseous phases. For water molecules, the condensed phase is more enriched while the vapor is more depleted. For example, rain condensing from a cloud will be heavier than the vapor starting point. Generally, the large variations in deuterium concentrations of water are from the fractionations between liquid, vapor, and solid reservoirs.
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The fractionation of sulfur and oxygen isotopes during microbial sulfide oxidation (MSO) has been studied to assess its potential as a proxy to differentiate it from the abiotic oxidation of sulfur. The light isotopes of the elements that are most commonly found in organic molecules, such as 12C, 16O, 1H, 14N and 32S, form bonds that are broken more easily than bonds between the corresponding heavy isotopes, 13C, 18O, 2H, 15N and 34S . Because there is a lower energetic cost associated with the use of light isotopes, enzymatic processes usually discriminate against the heavy isotopes, and, as a consequence, biological fractionations of isotopes are expected between the reactants and the products. A normal kinetic isotope effect is that in which the products are depleted in the heavy isotope relative to the reactants (low heavy isotope to light isotope ratio), and although this is not always the case, the study of isotope fractionations between enzymatic processes may allow tracing the source of the product.
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Iron is also important in plants, given that they need iron to transfer electrons during photosynthesis. Finally, in animals, iron plays many roles, however, its most essential function is to transport oxygen in the bloodstream throughout the body. Thus, iron undergoes many biological processes, each of which have variations in which isotopes of iron they preferentially use. While iron isotopic fractionations are observed in many organisms, they are still not well understood.
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In addition to observational studies of animal behavior, and quantification of animal stomach contents, trophic level can be quantified through stable isotope analysis of animal tissues such as muscle, skin, hair, bone collagen. This is because there is a consistent increase in the nitrogen isotopic composition at each trophic level caused by fractionations that occur with the synthesis of biomolecules; the magnitude of this increase in nitrogen isotopic composition is approximately 3–4‰.
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Biological deuterium fractionation through metabolism is very organism and pathway dependent, resulting in a wide variability in fractionations. Despite this, some trends still hold. Hydrogen isotopes tend to fractionate very strongly in autotrophs relative to heterotrophs during lipid biosynthesis - chemoautotrophs produce extremely depleted lipids, with the fractionation ranging from roughly −200 to −400‰. This has been observed both in laboratory-grown cultures fed a known quantity of deuterated water and in the environment.
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Lipid biosynthesis is biochemically complex, involving multiple enzyme-dependent steps that can lead to isotope fractionations. There are three major pathways of lipid biosynthesis, known as the mevalonate pathway, the acetogenic pathway, and the 1-deoxyD-xylulose-5-phosphate/2-methylerythroyl-4-phosphate pathway. The acetogenic pathway is responsible for the production of n-alkyl lipids like leaf waxes, and is associated with a smaller δD depletion relative to source water than the other two lipid biosynthesis pathways.
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Further experiments on unicellular algae Eudorina unicocca and Volvox aureus show no effect of growth rate (controlled by nitrogen limitation) on fatty acid δD. However, sterols become more D-depleted as growth rate increases, in agreement with alkenone isotopic composition in coccolithophores. Overall, although there are some strong trends with lipid δD, the specific fractionations are compound-specific. As a result, any attempt to create a salinometer through δD measurements will necessarily be specific to a single compound type.
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In each step they found deuterium further depleted. A landmark paper in 1980 by Marilyn Epstep, now M. Fogel, and Thomas Hoering titled "Biogeochemistry of the stable hydrogen isotopes" refined the links between organic materials and sources. In this early stage of hydrogen stable isotope study, most isotope compositions or fractionations were reported as bulk measurements of all organic material or all inorganic material. Some exceptions include cellulose and methane, as these compounds are easily separated.
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The H isotopic composition of photoautotrophs can be estimated using the equation below: :, where , and are the D/H ratios of lipids, water, and substrates, respectively. is the mole fraction of lipid H derived from external water, whereas and denote the net isotopic fractionations associated with uptake and utilization of water and substrate hydrogen, respectively. For Phototrophs, is calculated assuming that equals to 1. The isotopic fractionation between lipids and methane () is 0.94 for fatty acids and 0.79 for isoprenoid lipids.
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Hydrogen isotope fractionation in the hydrological cycle (modified from hydrological cycle diagram). Isotope fractionations are calculated as difference between product and source water in each process, at typical temperature and humidity conditions. Water is the primary source of hydrogen to all living organisms, so the isotopic composition of environmental water is a first-order control on that of the biosphere. The hydrological cycle moves water around different reservoirs on the surface of the earth, during which hydrogen isotopes in water are significantly fractionated.
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He received his Ph.D. in Uppsala 1957 with the thesis Zone electrophoresis in columns and adsorption chromatography on ionic cellulose derivatives as methods for peptide and protein fractionations: application to the study of posterior pituitary hormones. The separation method for which Porath is most well known is gel filtration, which he developed together with Per Flodin. Flodin worked with dextran research at Pharmacia. In 1957, Porath discovered that columns filled with dextran gel could be used as "molecular sieves" to separate biomolecules by size.
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Proteins, however, do not follow as significant a trend, with both heterotrophs and autotrophs capable of generating large and variable fractionations. In part, kinetic fractionation of the lighter isotope during formation of reducing equivalents NADH and NADPH result in lipids and proteins that are isotopically lighter. Salinity appears to play a role in the degree of deuterium fractionation as well; more saline waters affect growth rate, the rate of hydrogen exchange, and evaporation rate. All of these factors influence lipid δD upon hydrogen being incorporated into biomass.
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This shift would have led to an incredible increase in sulfate weathering which would have led to an increase in sulfate in the oceans. The large isotopic fractionations that would likely be associated with bacteria reduction are produced for the first time. Although there was a distinct rise in seawater sulfate at this time it was likely still only less than 5–15% of present-day levels. At 1.8 Ga, Banded iron formations (BIF) are common sedimentary rocks throughout the Archean and Paleoproterozoic; their disappearance marks a distinct shift in the chemistry of ocean water.
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The δD values of alkenones are highly correlated to the δD values of sea water, and therefore can be used to reconstruct paleoenvironmental properties that constrain the isotopic composition of sea water. The most notable reconstruction that alkenone δD values are applied to is the salinity of ancient oceans. Scanning electron micrograph of a single Emiliana huxleyi cell. Both the δD values of sea water and the fractionations associated with hyptophyte biochemistry (εbio) are fairly well understood, so alkenones can be readily used to observe the secondary effect of salinity on δD.
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The hydrogen isotope composition of oil, gas and coal is an important geochemical tool to study the formation, storage, migration and many other processes. The hydrogen isotopic signal of fossil fuels results from both inheritance of source material and water as well as fractionations during hydrocarbon generation and subsequent alteration by processes such as isotopic exchange or biodegradation. When interpreting hydrogen isotopic data of sedimentary organic matter one must take all the processes that might have an isotope effect into consideration. Almost all of the organic hydrogen is exchangeable to some extent.
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Equilibrium isotope fractionation is the partial separation of isotopes between two or more substances in chemical equilibrium. Equilibrium fractionation is strongest at low temperatures, and (along with kinetic isotope effects) forms the basis of the most widely used isotopic paleothermometers (or climate proxies): D/H and 18O/16O records from ice cores, and 18O/16O records from calcium carbonate. It is thus important for the construction of geologic temperature records. Isotopic fractionations attributed to equilibrium processes have been observed in many elements, from hydrogen (D/H) to uranium (238U/235U).
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The use of iron isotopes may also have applications when studying potential evidence for life on other planets. The ability of microbes to utilize iron in their metabolisms makes it possible for organisms to survive in anoxic, iron-rich environments, such as Mars. Thus, the continual improvement of knowledge regarding the biological fractionations of iron observed on Earth can have applications when studying extraterrestrial samples in the future. While this field of research is still developing, this could provide evidence regarding whether a sample was generated as a result of biologic or abiologic processes depending on the isotopic fractionation.
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Certain isotopes of trace metals are preferentially oxidized or reduced; thus, transitions between redox species of the metal ions (e.g., Fe2+ → Fe3+) are fractionating, resulting in different isotopic compositions between the different redox pools in the environment. Additionally, at high temperatures, metals ions can evaporate (and subsequently condense upon cooling), and the relative differences in isotope masses of a given heavy metal leads to fractionation during these evaporation and condensation processes. Diffusion of isotopes through a solution or material can also result in fractionations, as the lighter mass isotopes are able to diffuse at a faster rate.
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It has also been suggested that BIFs may be biologic in origin. The range of their δ56/54Fe values fall within the range of those observed to occur as a result of biologic processes relating to bacterial metabolic processes, such as those of anoxygenic phototrophic iron- oxidizing bacteria. Ultimately, the improved understanding of BIFs using iron isotope fractionations would allow for the reconstruction of past environments and the constraint of processes occurring on the ancient Earth. However, given that the values observed as a result of biogenic and abiogenic fractionation are relatively similar, the exact processes of BIFs are still unclear.
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Sulfate-reducing bacteria metabolize 32S more readily than 34S, resulting in an increase in the value of the δ34S in the remaining sulfate in the seawater. Archean pyrite found in barite in the Warrawoona Group, Western Australia, with sulfur fractionations as great as 21.1‰ hint at the presence of sulfate-reducers as early as . The δ34S value, recorded by sulfate in marine evaporites, can be used to chart the sulfur cycle throughout earth's history. The Great Oxygenation Event around altered the sulfur cycle radically, as increased atmospheric oxygen permitted an increase in the mechanisms that could fractionate sulfur isotopes, leading to an increase in the δ34S value from ~0‰ pre-oxygenation.
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Duplessy turned to the ocean because of its role as a climate regulator and its major impact on biogeochemical cycles, particularly the carbon cycle. His doctoral thesis work has focused on the geochemistry of stable carbon isotopes in the sea.Duplessy J.C., La géochimie des isotopes stables du carbone dans la mer, Université de Paris VI, Thèse de doctorat ès Sciences Physiques, 21 juin 1972 He showed how the distribution of the stable heavy carbon isotope, carbon-13, was governed by biological fractionations related to chlorophyll assimilation by phytoplankton, then by ocean circulation and finally, to a lesser extent, by gas exchanges between the ocean and the atmosphere. All these phenomena, which dominate the carbon cycle in the ocean, are now being taken into account to study the fate of carbon dioxide emitted by human activities.
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477-482 The deep waters of the world ocean are formed by convection and diving of dense surface waters during winter periods. To understand the causes of changes in deep ocean circulation, it was necessary to develop a method to reconstruct not only the temperature (which was already known), but also the salinity of surface waters in the past. Duplessy has developed a method based on fractionations that affect stable oxygen isotopes during the water cycle. This has allowed him to reconstruct the salinity of the Atlantic Ocean during the last glacial maximum with sufficient accuracy for major modelling groups to use this data to simulate global ocean circulation using general ocean circulation models.Duplessy J. C. et a, « Surface salinity reconstruction of the North Atlantic Ocean during the last glacial maximum », Oceanologica Acta, 1991, 14, p.
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