Mitchell A D, Benevenga N J
J Nutr. 1978 Jan;108(1):67-78. doi: 10.1093/jn/108.1.67.
The role of transamination as the initial step in catabolism of methionine in the rat was investigated. [Methyl-14C] or [1-14C]-L-Methionine was added to tissue homogenates and transamination was determined from the counts recovered in a precipitable phenylhydrazone following treatment of the samples with 2,4-dinitrophenylhydrazine. Transamination of methionine was detected in homogenates of liver, kidney, heart, brain, spleen, skeletal muscle, and small intestines. The product of methionine transamination in the liver was identified as alpha-keto-gamma-methiolbutyrate. Approximately the same tissue distribution was observed for the conversion of the methyl or carboxyl carbon of methionine or alpha-keto-gamma-methiolbutyrate to CO2. alpha-Keto-butyrate could be used as a co-substrate for transamination, but inhibited oxidation of methionine apparently by competing for oxidation of alpha-keto-gamma-methiolbutyrate. S-Adenosyl-L-methionine was not a substrate for transamination in the liver homogenate system nor did it inhibit transamination of methionine. Amino-oxyacetic acid inhibited transamination and oxidation of methionine, but not oxidation of alpha-keto-gamma-methiolbutyrate. These observations are consistent with transamination being an initial step in methionine catabolism and an alternate pathway for methionine oxidation which does not involve its activation to S-adenosyl-L-methionine.
研究了转氨作用作为大鼠体内蛋氨酸分解代谢第一步的作用。将[甲基-14C]或[1-14C]-L-蛋氨酸添加到组织匀浆中，在用2,4-二硝基苯肼处理样品后，通过可沉淀苯腙中回收的计数来测定转氨作用。在肝脏、肾脏、心脏、大脑、脾脏、骨骼肌和小肠的匀浆中检测到了蛋氨酸的转氨作用。肝脏中蛋氨酸转氨作用的产物被鉴定为α-酮基-γ-甲硫基丁酸。对于蛋氨酸或α-酮基-γ-甲硫基丁酸的甲基或羧基碳向二氧化碳的转化，观察到了大致相同的组织分布。α-酮基丁酸可用作转氨作用的共底物，但显然通过竞争α-酮基-γ-甲硫基丁酸的氧化而抑制蛋氨酸的氧化。S-腺苷-L-蛋氨酸在肝脏匀浆系统中不是转氨作用的底物，也不抑制蛋氨酸的转氨作用。氨基氧乙酸抑制蛋氨酸的转氨作用和氧化，但不抑制α-酮基-γ-甲硫基丁酸的氧化。这些观察结果与转氨作用是蛋氨酸分解代谢的第一步以及蛋氨酸氧化的一条不涉及将其激活为S-腺苷-L-蛋氨酸的替代途径一致。
