Mechanism of the glycine cleavage reaction. Properties of the reverse reaction catalyzed by T-protein.
Mechanism of the glycine cleavage reaction. Properties of the reverse reaction catalyzed by T-protein.
复制标题
甘氨酸裂解反应的机制。
DOI：
10.1016/s0021-9258(18)48307-x
复制
发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Y. Motokawa
中科院分区：
文献类型：
--
作者：
K. Okamura;K. Fujiwara;Y. Motokawa
t蛋白是甘氨酸裂解系统的一个组成部分，它催化四氢叶酸亚甲基、氨和具有还原脂酰基的h蛋白合成h蛋白结合的中间体(Okamura-Ikeda， K., Fujiwara， K., and Motokawa， Y. (1982) J. Biol。化学，257,135-139)。光谱研究表明，只有在三种底物存在的情况下，亚甲基四氢叶酸才会被利用，这表明形成了一个四元配合物。亚甲基四氢叶酸的消耗量等于附着在h蛋白上的亚甲基碳的消耗量。稳态动力学研究表明，该反应是通过有序Ter - Bi机理进行的。还原h蛋白是与t蛋白结合的第一个底物，其次是亚甲基四氢叶酸和氨。产物的释放顺序为四氢叶酸和h蛋白结合的中间体。h蛋白、亚甲基四氢叶酸和氨的Km值分别为0.55微米、0.32毫米和22毫米。
T-protein, one of the components of the glycine cleavage system, catalyzes the synthesis of the H-protein-bound intermediate from methylenetetrahydrofolate, ammonia, and H-protein having a reduced lipoyl prosthetic group (Okamura-Ikeda, K., Fujiwara, K., and Motokawa, Y. (1982) J. Biol. Chem. 257, 135-139). Spectroscopic studies indicated that the utilization of methylenetetrahydrofolate occurred only in the presence of the three substrates, indicating the formation of a quaternary complex. The amount of methylenetetrahydrofolate consumed was equal to that of methylene carbon attached to H-protein. Steady-state kinetic studies show that the reaction proceeds through an Ordered Ter Bi mechanism. Reduced H-protein is the first substrate that binds T-protein followed by methylenetetrahydrofolate and ammonia. The order of release of products is tetrahydrofolate and the H-protein-bound intermediate. Km values for H-protein, methylenetetrahydrofolate, and ammonia are 0.55 microM, 0.32 mM, and 22 mM, respectively.