Storch K J, Wagner D A, Burke J F, Young V R
Laboratory of Human Nutrition, School of Science, Massachusetts Institute of Technology, Cambridge 02139.
Am J Physiol. 1990 May;258(5 Pt 1):E790-8. doi: 10.1152/ajpendo.1990.258.5.E790.
Methionine (Met) conservation in healthy young adult men (4/diet group) was explored by supplying one of the following three L-amino acid based diets: 1) adequate Met but no cystine; 2) neither Met nor cystine; or 3) no Met but cystine supplementation. After 5 days, subjects received a continuous intravenous infusion of L-[1-13C; methyl-2H3]Met for 5 h while the diet was given as small isocaloric isonitrogenous meals. Estimates were made of rates of Met incorporation into protein synthesis (S) and release from body proteins (B), transmethylation (TM), remethylation of homocysteine (RM), and transsulfuration (TS). For the adequate Met diet, the rates were S = 24 +/- 2, B = 18 +/- 1, TM = 12.4 +/- 1.7, RM = 4.7 +/- 1.1, and TS = 7.6 +/- 0.6 (SE) mumol.kg-1.h-1. The sulfur amino acid-devoid diet significantly (P less than 0.05) reduced S, TM, RM, and TS. Supplementation of this diet with cystine reduced Met oxidation (P = 0.05). Therefore, two loci are quantitatively important regulatory points in Met conservation in vivo: 1) the distribution of Met between the pathways of protein anabolism and TM (Met locus) and 2) the distribution of homocysteine between RM and TS (homocysteine locus).
通过提供以下三种基于L-氨基酸的饮食之一，研究了健康年轻成年男性（4/饮食组）中蛋氨酸（Met）的保留情况：1）蛋氨酸充足但无胱氨酸；2）既无蛋氨酸也无胱氨酸；或3）无蛋氨酸但补充胱氨酸。5天后，受试者接受5小时的L-[1-¹³C；甲基-²H₃]蛋氨酸持续静脉输注，同时饮食以等热量、等氮量的小餐形式给予。对蛋氨酸掺入蛋白质合成（S）和从身体蛋白质释放（B）、转甲基作用（TM）、同型半胱氨酸的再甲基化（RM）以及转硫作用（TS）的速率进行了估计。对于蛋氨酸充足的饮食，速率分别为S = 24 ± 2、B = 18 ± 1、TM = 12.4 ± 1.7、RM = 4.7 ± 1.1以及TS = 7.6 ± 0.6（SE）μmol·kg⁻¹·h⁻¹。缺乏含硫氨基酸的饮食显著（P < 0.05）降低了S、TM、RM和TS。用胱氨酸补充这种饮食可降低蛋氨酸氧化（P = 0.05）。因此，在体内蛋氨酸保留方面有两个定量重要的调控点：1）蛋氨酸在蛋白质合成代谢途径和转甲基作用之间的分配（蛋氨酸位点）以及2）同型半胱氨酸在再甲基化和转硫作用之间的分配（同型半胱氨酸位点）。
