Storch K J, Wagner D A, Young V R
Laboratory of Human Nutrition, School of Science, Massachusetts Institute of Technology, Cambridge.
Am J Clin Nutr. 1991 Aug;54(2):386-94. doi: 10.1093/ajcn/54.2.386.
The effects of a daily 3-g supplement of betaine on kinetic aspects of L-[2H3-methyl-1-13C]methionine (MET) metabolism in healthy young adult men were explored. Four groups of four subjects each were given a control diet, based on an L-amino acid mixture supplying 29.5 and 21.9 mg.kg-1.d-1 of L-methionine and L-cystine for 4 d before the tracer study, conducted on day 5 during the fed state. Two groups received the control diet and two groups received the betaine supplement. Tracer was given intravenously (iv) or orally. The transmethylation rate of MET (TM), homocysteine remethylation (RM), and oxidation of methionine were estimated from plasma methionine labeling and 13C enrichment of expired air. RM tended to increase (P = 0.14) but the TM and methionine oxidation were significantly (P less than 0.05) higher after betaine supplementation when estimated with the oral tracer. No differences were detected with the intravenous tracer. Methionine concentration in plasma obtained from blood taken from subjects in the fed state was higher (P less than 0.01) with betaine supplementation. These results suggest that excess methyl-group intake may increase the dietary requirement for methionine.
探讨了每日补充3克甜菜碱对健康年轻成年男性L-[2H3-甲基-1-13C]蛋氨酸（MET）代谢动力学方面的影响。四组，每组四名受试者，在示踪剂研究前4天给予基于L-氨基酸混合物的对照饮食，该混合物提供29.5和21.9毫克·千克-1·天-1的L-蛋氨酸和L-胱氨酸，示踪剂研究在第5天进食状态下进行。两组接受对照饮食，两组接受甜菜碱补充剂。示踪剂通过静脉注射（iv）或口服给予。根据血浆蛋氨酸标记和呼出气体的13C富集情况估算MET的转甲基率（TM）、同型半胱氨酸再甲基化（RM）和蛋氨酸氧化。口服示踪剂估算时，补充甜菜碱后RM有增加趋势（P = 0.14），但TM和蛋氨酸氧化显著升高（P < 0.05）。静脉注射示踪剂时未检测到差异。补充甜菜碱后，进食状态下受试者血液中血浆蛋氨酸浓度更高（P < 0.01）。这些结果表明，过量甲基摄入可能会增加对蛋氨酸的饮食需求。
