N-Isotopic Composition in Human Plasma Protein Amino Acids at Natural Abundance Level and After a Single [15N2]urea Administration Measured by GC-C-IRMS

Abstract The GC-C-IRMS technique represents a new and useful tool to study the 15N abundance in amino acids for metabolic studies. Here we present 15N analysis data for 13 human plasma protein amino acids at natural abundance and in slightly enriched samples using GC-C-IRMS analysis of N-pivaloyl-i-propyl esters of amino acids. A mean precision of ± 0.71‰ Δ15N or ±0.77‰ Δ15N was determined for all amino acids analysed at natural abundance values and for the slightly enriched samples (< 100‰ δ15N), respectively. However, for individual amino acids at natural abundance derivatized and injected in duplicate the standard deviation ranged from 0.24 to 1.49‰. The lowest natural 15N abundance was found for threonine (about - 5‰ δ15N) and the highest for proline and glutamic acid (about 15‰ δ15N). A standard deviation (SD) range of±0.71 (glutamic acid) to ± 4.35 ‰ δ15N (phenylalanine) (mean SD = ± 1.at δ15N) was obtained in protein amino acids in a group of 7 volunteers at natural abundance level. A single oral [...