SIGNIFICANCE OF N¹⁵EXCESS IN NITROGENOUS COMPOUNDS OF BIOLOGICAL ORIGIN

Abstract

The purpose of this study was to determine whether the small increase in abundance of N15 normally found in nitrogenous compounds of biological origin is primarily due to mass discrimination in nitrogen metabolism, or to reproducible analytical errors.This problem was approached by repeatedly determining N15 in the same series of nine amino acids, either purchased in chromatographically pure form or isolated from proteins of rat liver, dog serum, and six plant sources. Proteins and amino acids included in the study were selected on the premise that concentration or redistribution of N15 might occur in such processes in urea formation, nitrogen transfer, or nitrogen fixation. Data for N15 excess in a series of alkaloids were also secured.Standard deviations obtained in series of analyses were too small, and values for N15 excess in the same amino acids isolated from different sources too variable, to permit interpreting the observed N15 excess as a reproducible error. Distribution of N15 in amino acids of the animal proteins studied resembled that observed when N15-labelled amino acids or ammonium compounds are given. Differences between results for amino acids of animal and plant origin also supported the idea that the small excess of N15 normally found is metabolically as well as statistically significant. Results for N15 in amide nitrogen likewise supported this view. The smallest excess of N15 occurred in amino acids from proteins of legumes, which fix nitrogen. In synthetic amino acids, the concentration of N15 was more often below than above normal abundance.

Variability of Anaerobic Animal Waste Lagoon delta15N Source Signatures

“…This extensive database of isotopically light N inputs emphasizes that isotopic N discrimination of animal waste sources in groundwater are solely dependent upon the isotopic enrichment that occurs after excretion. These results differ from those of Kreitler (1975) who suggested that the δ 15 N of the excreted urea is 8‰ lighter than the N content of the feed which was assumed to be +5‰ (Gaebler et al, 1963).…”

Isotope Effects of Nitrogen in the Soil and Biosphere

“…Two other, but older papers by Gaebler et al (1963) should also be mentioned in this connection. As a rough estimate one can show that our planet earth is presently populated with about 4.5 X 10 9 people which equals a biomass of about 6.44 X 10 7 t (Lieth and Whittaker, 1975) and supposing a C/N ratio of about 7 this yields about 4.6 X 10 6 t N. Comparing this value with figures in Table 9-2 one realizes that this nitrogen pool does not play an important role in the biogeochemical cycles of chemical elements and their isotopes.…”

Embracing variability in amino acid δ15N fractionation: mechanisms, implications, and applications for trophic ecology

“…Gaebler et al. (, ) were likely the first to document differential δ 15 N fractionation in AAs, showing that while some AAs exhibited large offsets in 15 N excess in rat liver compared with diet, other AAs exhibited little or no isotope difference. Hare et al.…”

“…McMAHoN AND McCArTHy Differential 15 N enrichment of individual AAs with trophic transfer is at the heart of the CSIA-AA approach to studying trophic ecology. Gaebler et al (1963Gaebler et al ( , 1966 were likely the first to document differential δ 15 N fractionation in AAs, showing that while some AAs exhibited large offsets in 15 N excess in rat liver compared with diet, other AAs exhibited little or no isotope difference. Hare et al (1991) also observed similar δ 15 N offsets in a smaller set of collagen AAs from pigs fed different diets.…”