Fuller Benjamin T, Petzke Klaus J
Department of Archaeology and Anthropology, University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing, 100049, China.
Department of Physiology of Energy Metabolism, German Institute of Human Nutrition in Potsdam-Rehbruecke (DIfE), Arthur-Scheunert-Allee 114-116, D-14558, Nuthetal, Germany.
Rapid Commun Mass Spectrom. 2017 Apr 30;31(8):705-718. doi: 10.1002/rcm.7835.
Nitrogen stable isotope ratios (δ N values) are used to reconstruct dietary patterns, but the biochemical mechanism(s) responsible for the diet to tissue trophic level effect and its variability are not fully understood. Here δ N amino acid (AA) values and physiological measurements (nitrogen intake, plasma albumin concentrations, liver-reduced glutathione concentrations and leucine oxidation rates) are used to investigate increased dietary protein consumption and oxidative stress (vitamin E deficiency) in rat total plasma protein.
Using gas chromatography/combustion/isotope ratio mass spectrometry, the δ N values from N-pivaloyl-i-propyl esters of 15 AAs are reported for rats (n = 40) fed casein-based diets with: adequate protein (AP, 13.8%; n = 10), medium protein (MP, 25.7%; n = 10), high protein (HP, 51.3%; n = 10) or HP without vitamin E (HP-E; n = 10) for 18 weeks.
Between the HP and AP groups, the δ N values of threonine (-4.0‰), serine (+1.4‰) and glycine (+1.2‰) display the largest differences and show significant correlations with: nitrogen intake, plasma albumin concentrations, liver-reduced glutathione concentrations and leucine oxidation rates. This indicates increased AA catabolism by the dietary induction of shared common metabolic pathways involving the enzymes threonine ammonia-lyase (EC 4.3.1.19), serine hydroxymethyltransferase (EC 2.1.2.1) and the glycine cleavage system (EC 2.1.2.10). The δ N values of the HP-E and HP groups were not found to be significantly different.
The N-depleted results of threonine are linked to increased activity of threonine ammonia-lyase, and show potential as a possible biomarker for protein intake and/or gluconeogenesis. We hypothesize that the inverse nitrogen equilibrium isotope effects of Schiff base formation, between AAs and pyridoxal-5'-phosphate cofactor enzymes, play a key role in the bioaccumulation and depletion of N in the biomolecules of living organisms and contributes to the variability in the nitrogen trophic level effect. Copyright © 2017 John Wiley & Sons, Ltd.
氮稳定同位素比率（δN值）用于重建饮食模式，但饮食对组织营养级效应及其变异性的生化机制尚未完全明确。本文采用δN氨基酸（AA）值和生理测量指标（氮摄入量、血浆白蛋白浓度、肝脏还原型谷胱甘肽浓度和亮氨酸氧化率），研究大鼠总血浆蛋白中饮食蛋白质消耗增加和氧化应激（维生素E缺乏）的情况。
使用气相色谱/燃烧/同位素比率质谱法，报告了40只大鼠（每组10只）在18周内喂食基于酪蛋白的饮食后的15种氨基酸的N-新戊酰基-i-丙酯的δN值，这些饮食包括：适量蛋白质（AP，13.8%）、中等蛋白质（MP，25.7%）、高蛋白（HP，51.3%）或不含维生素E的高蛋白（HP-E）。
在HP组和AP组之间，苏氨酸（-4.0‰）、丝氨酸（+1.4‰）和甘氨酸（+1.2‰）的δN值差异最大，并且与氮摄入量、血浆白蛋白浓度、肝脏还原型谷胱甘肽浓度和亮氨酸氧化率显著相关。这表明通过饮食诱导涉及苏氨酸氨裂合酶（EC 4.3.1.19）、丝氨酸羟甲基转移酶（EC 2.1.2.1）和甘氨酸裂解系统（EC 2.1.2.10）的共同代谢途径，导致氨基酸分解代谢增加。未发现HP-E组和HP组的δN值有显著差异。
苏氨酸的氮消耗结果与苏氨酸氨裂合酶活性增加有关，并显示出作为蛋白质摄入量和/或糖异生可能生物标志物的潜力。我们推测，氨基酸与磷酸吡哆醛辅因子酶之间席夫碱形成的反向氮平衡同位素效应，在生物体生物分子中氮的生物积累和消耗中起关键作用，并导致氮营养级效应的变异性。版权所有© 2017约翰威立父子有限公司。
