GOT2 dimer transfers amino group from L-Cys to 2OG to form 3MPYR and Glu

Hydrogen sulfide (H2S) produced endogenously has been established as the third gaseous signaling molecule, a smooth muscle relaxant and a neuroprotectant (Kimura 2011a, 2011b). Three human enzyme systems produce H2S in the brain, retina and vascular endothelial cells. 3-mercaptopyruvate sulphurtransferase (MPST, aka 3MST) in conjunction with cysteine (aspartate) aminotransferase (CAT, aka GOT2) is decribed here. The first step is the reversible transamination between L-cysteine (L-Cys) and 2-oxoglutarate (2OG, aka alpha-ketoglutarate) to form 3-methylpyruvate (3MPYR) and glutamate (Glu) catalysed by GOT2. Two forms of human aspartate aminotransferase (GOT) enzymes exist; cytosolic (GOT1) and mitochondrial (GOT2). Both are dimeric proteins requiring pyridoxal phosphate for activity. Human GOT2 (Zhou et al. 1998) possesses the same catalytic activity as its rat counterpart (Ubuka et al. 1978).

内生性产生的硫化氢（H2S）已被确认为第三种气体信号分子，具有平滑肌松弛剂和神经保护剂的作用（Kimura 2011a, 2011b）。人脑、视网膜和血管内皮细胞中存在三种酶系统以产生H2S。本文所述为3-巯基丙酮酸硫转移酶（MPST，亦称3MST）与半胱氨酸（天冬氨酸）转氨酶（CAT，亦称GOT2）的联合作用。反应的第一步是L-半胱氨酸（L-Cys）与2-酮戊二酸（2OG，亦称α-酮戊二酸）之间的可逆转氨反应，生成3-甲基丙酮酸（3MPYR）和谷氨酸（Glu），此过程由GOT2催化。人类天冬氨酸转氨酶（GOT）酶存在两种形式；细胞质型（GOT1）和线粒体型（GOT2）。两者均为二聚蛋白，需要吡哆醛磷酸盐以维持其活性。人类GOT2（Zhou et al. 1998）与其大鼠同源物（Ubuka et al. 1978）具有相同的催化活性。