TDH tetramer oxidises L-Thr to 2A-3OB

The degradation of L-threonine to glycine in both prokaryotes and eukaryotes takes place through a two-step biochemical pathway. In the first step, L-threonine (L-Thr) is oxidised to 2-amino-3-oxobutanoate (2A-3OBU) using NAD+ as acceptor. This reaction is catalysed by mitochondrial L-threonine 3-dehydrogenase (TDH) (Edgar 2002). The human activity is inferred from the characterised porcine Tdh (Edgar 2002b, Kao & Davis 1994). TDH is thought to exist as a tetramer on the mitochondrial inner membrane in complex with dimeric 2-amino-3-ketobutyrate coenzyme A ligase (GCAT), the second enzyme in this pathway (Tressel et al. 1986). With these two enzymes located together, it stops the rapid and spontaneous decarboxylation of 2A-3OBU to aminoacetone and carbon dioxide and instead, results in glycine formation.

在原核生物和真核生物中，L-苏氨酸降解为甘氨酸的过程通过一个两步生化途径进行。首先，L-苏氨酸（L-Thr）在NAD+作为受体的作用下被氧化为2-氨基-3-氧丁酸（2A-3OBU）。此反应由线粒体L-苏氨酸3-脱氢酶（TDH）（Edgar 2002）催化。人类活动是通过已表征的猪Tdh（Edgar 2002b，Kao & Davis 1994）推断得出的。TDH被认为存在于线粒体内膜上，作为四聚体与二聚体的2-氨基-3-酮丁酸辅酶A连接酶（GCAT）复合，这是该途径中的第二种酶（Tressel et al. 1986）。这两种酶的共定位阻止了2A-3OBU快速自发脱羧为氨基乙酮和二氧化碳，从而促使甘氨酸的形成。