Mechanism of the glycine cleavage reaction. Properties of the reverse reaction catalyzed by T-protein.
1987; Elsevier BV; Volume: 262; Issue: 14 Linguagem: Inglês
10.1016/s0021-9258(18)48307-x
ISSN1083-351X
AutoresKazuko Okamura‐Ikeda, Kazuko Fujiwara, Y. Motokawa,
Tópico(s)Polyamine Metabolism and Applications
Resumofrom 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.K , values for H-protein, methylenetetrahydrofolate, and ammonia are 0.55 PM, 0.32 mM, and 22 mM, respectively.The glycine cleavage system is a multicomponent enzyme system and catalyzes the cleavage of glycine to yield carbon dioxide, ammonia, 5,10-CHz-H,folate,' and one reducing equivalent as NADH + H' (1).The system consists of three enzymes, P-protein, T-protein, and L-protein, and a carrier protein, which is designated H-protein and contains covalently bound lipoic acid.The catalytic pathway as it is presently understood is described by Equations 1-4 (2-5).P-protein CHz(NHz)COOH + H-protein-lipoylS, -. co, + H-protein-lipoyl(SH)S-CH~NH, T-protein H-protein-lipoyl(SH)S-CHzNHz + H,folate -NHs + 5,
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