ISOTOPE EFFECTS IN METABOLISM OF<sup>14</sup>N AND<sup>15</sup>N FROM UNLABELED DIETARY PROTEINS

Gaebler, O. H.; Vitti, Trieste G.; Vukmirovich, Robert

doi:10.1139/o66-142

Cited by 147 publications

(107 citation statements)

References 6 publications

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“…Significant isotope fractionation (e AA ) was measured for five AAs (Asp, Glu, Ile, Phe, and Ser; linear regression, p , 0.05), with a mean e AA (6 SEM) of 5.5 6 0.5% determined using analysis of covariance (ANCOVA; p , 0.001). This e AA value is similar to that measured by Gaebler et al (1966) for deamination (i.e., the removal of NH 2 from AAs) and to e values measured by Silfer et al (1992) for protein hydrolysis (e 5 2.5-4%). Both processes likely drive protein degradation at depth.…”

Section: Resultssupporting

confidence: 85%

Midwater zooplankton and suspended particle dynamics in the North Pacific Subtropical Gyre: A stable isotope perspective

Hannides

Popp

Choy

et al. 2013

Limnology & Oceanography

156

147

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We used amino acid (AA) compound-specific isotope analysis (d 15 N AA and d 13 C AA values) of midwater zooplankton and suspended particles to examine their dynamics in the mesopelagic zone. Suspended particle d 15 N AA values increased by up to 14% with depth, whereas particle trophic status (measured as trophic position, TP) remained constant at 1.6 6 0.07. Applying a Rayleigh distillation model to these results gave an observed kinetic isotope fractionation of 5.7 6 0.4%, similar to that previously measured for protein hydrolysis. AA-based degradation index values also decreased with depth on the particles, whereas a measure of heterotrophic resynthesis (SV) remained constant at 1.2 6 0.3. The main mechanism driving 15 N enrichment of suspended particles appears to be isotope fractionation associated with heterotrophic degradation, rather than a change in trophic status or N source with depth. In zooplankton the ''source'' AA phenylalanine (Phe) became 15 N enriched by up to 3.5% with depth, whereas zooplankton TP increased by up to 0.65 between the surface ocean and midwaters. Both changes in the d 15 N values of food resources at the base of the zooplankton food web and changes in zooplankton TP drive observed zooplankton 15 N enrichment with depth. Midwater zooplankton d 15 N Phe values were lower by 5-8% compared with suspended particles, indicating this organic matter pool is not a significant zooplankton food resource at depth. Instead, 62-88% of the N sustaining midwater zooplankton is surface derived, obtained through consumption of sinking particles, carnivory of vertical migrants, or direct feeding in surface waters at night.

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Section: Resultssupporting

confidence: 85%

Midwater zooplankton and suspended particle dynamics in the North Pacific Subtropical Gyre: A stable isotope perspective

Hannides

Popp

Choy

et al. 2013

Limnology & Oceanography

156

147

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“…Several authors have suggested that the fractionation of nitrogen isotopes most likely occurs during the deamination and transamination of amino acids (e.g. Gaebler et al, 1966;Minagawa and Wada, 1984). Enzymatic processes necessary for homeostasis may then lead to even higher enrichments of heavy nitrogen within tissues.…”

Section: Discussionmentioning

confidence: 99%

Nitrogen stress causes unpredictable enrichments of 15N in two nectar-feeding bat species

Voigt

Matt

2004

Journal of Experimental Biology

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SUMMARY We estimated the effect of nitrogen stress on the nitrogen isotope enrichments in wing membrane and blood of two nectar-feeding bats(Glossophaga soricina and Leptonycteris curasoae) by offering a nitrogen-poor diet with a high δ15N andδ 13C. Before the experiment, bats were sustained on a normal diet with a low δ15N and δ13C. Under this first food regime, the fractionation of nitrogen isotopes averaged 3.1‰δ 15N for blood and 4.4‰ δ15N for wing membrane, which was almost twice as high as the corresponding fractionation of carbon isotopes. After switching to the nitrogen-poor diet, the enrichment of heavy isotopes increased for both elements in all tissues under study. The recently published estimates of half-life of carbon isotopes indicated a low turnover rate of carbon in wing membrane and blood and an almost constant half-life over varying losses of body mass. The estimates of half-life of nitrogen were two to six times higher than those of carbon. We argue that this discrepancy was caused by the mixing of nitrogen isotopes from internal and external sources. The mixing effect was probably negligible for carbon as the amount of ingested carbon outweighed the amount of mobilized carbon from internal sources. A correlation between the estimated turnover rates of nitrogen and losses of body masses was probably obscured by the additional fractionation of nitrogen isotopes in catabolic animals. We conclude that the interpretation of nitrogen isotope data of free-ranging animals is difficult when the animal's diet is changing to a critical nitrogen content.

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“…There are also considerable fractionations during animal metabolism (e.g. Gaebler et al, 1963;Gaebler, Vitti & Vukmirovich, 1966), and N leaving the animal via urine is depleted in ^^N, thus the animal itself will become enriched (although a patch of recently deposited urine will likely be a site of NH^ volatilization and, therefore, subsequent enrichment). As a result, there is an average increase of c. 3-5 %" per trophic level (Minagawa & Wada, 1984).…”

Section: {I) N Metabolism In Plantsmentioning

confidence: 99%

Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems

1997

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summary Equilibrium and kinetic isotope fractionations during incomplete reactions result in minute differences in the ratio between the two stable X isotopes, 15N and 14N, in various N pools. In ecosystems such variations (usually expressed in per mil [δ15N] deviations from the standard atmospheric N2) depend on isotopic signatures of inputs and outputs, the input‐output balance, N transformations and their specific isotope effects, and compartmentation of N within the system. Products along a sequence of reactions, e.g. the N mineralization‐N uptake pathway, should, if fractionation factors were equal for the different reactions, become progressively depleted. However, fractionation factors van. For example, because nitrification discriminates against 15N in the substrate more than does N mineralization, NH4+can become isotopically heavier than the organic N from which it is derived. Levels of isotopic enrichment depend dynamically on the stoichiometry of reactions, as well as on specific abiotic and biotic conditions. Thus, the δ15N of a specific N pool is not a constant, and 15N of a N compound added to the system is not a conservative, unchanging tracer. This fact, together with analytical problems of measuring 15N in small and dynamic pools of N in the soil‐plant system, and the complexity of the X cycle itself (for instance the abundance of reversible reactions), limit the possibilities of making inferences based on observations of 15N abundance in one or a few pools of N in a system. Nevertheless, measurements of δ15N might offer the advantage of giving insights into the N cycle without disturbing the system by adding 15N tracer. Such attempts require, however, that the complex factors affecting 15N in plants be taken into account, viz. (i) the source(s) of N (soil, precipitation, NOX, NH3, N2‐fixation), (ii) the depth(s) in soil from which N is taken up, (iii) the form(s) of soil‐N used (organic N, NH4+, NO3−), (iv) influences of mycorrhizal symbioses and fractionations during and after N uptake by plants, and (v) interactions between these factors and plant phenology. Because of this complexity, data on δ15N can only be used alone when certain requirements are met, e.g. when a clearly discrete N source in terms of amount and isotopic signature is studied. For example, it is recommended that N in non‐N2‐fixing species should differ more than 5% from N derived by N2‐fixation, and that several non‐N2‐fixing references are used, when data on δ15N are used to estimate Na‐fixation in poorly described ecosystems. As well as giving information on N source effects, δ15N can give insights into N cycle rates. For example, high levels of N deposition onto previously N‐limited systems leads to increased nitrification, which produces 15N‐enriched NH4 and N‐depleted NO3. As many forest plants prefer NH4−they become enriched in 15N in such circumstances. This change in plant 15N will subsequently also occur in the soil surface horizon after litter‐fall, and might be a useful indicator of N saturation, especially since ...

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ISOTOPE EFFECTS IN METABOLISM OF¹⁴N AND¹⁵N FROM UNLABELED DIETARY PROTEINS

Cited by 147 publications

References 6 publications

Midwater zooplankton and suspended particle dynamics in the North Pacific Subtropical Gyre: A stable isotope perspective

Midwater zooplankton and suspended particle dynamics in the North Pacific Subtropical Gyre: A stable isotope perspective

Nitrogen stress causes unpredictable enrichments of 15N in two nectar-feeding bat species

Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems

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ISOTOPE EFFECTS IN METABOLISM OF14N AND15N FROM UNLABELED DIETARY PROTEINS

Cited by 147 publications

References 6 publications

Midwater zooplankton and suspended particle dynamics in the North Pacific Subtropical Gyre: A stable isotope perspective

Midwater zooplankton and suspended particle dynamics in the North Pacific Subtropical Gyre: A stable isotope perspective

Nitrogen stress causes unpredictable enrichments of 15N in two nectar-feeding bat species

Tansley Review No. 9515N natural abundance in soil‐plant systems

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ISOTOPE EFFECTS IN METABOLISM OF¹⁴N AND¹⁵N FROM UNLABELED DIETARY PROTEINS

Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems