Mechanism of the glycine cleavage reaction. Properties of the reverse reaction catalyzed by T-protein.
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.
D000594:Amino Acid Oxidoreductases; D050960:Aminomethyltransferase; D000641:Ammonia / Q000378:metabolism; D000643:Ammonium Chloride / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D050961:Glycine Decarboxylase Complex H-Protein; D050841:Glycine Dehydrogenase (Decarboxylating); D019877:Hydroxymethyl and Formyl Transferases; D007700:Kinetics; D011485:Protein Binding; D013763:Tetrahydrofolates / Q000378:metabolism / Q000494:pharmacology; D014166:Transferases / Q000378:metabolism*
D002352:Carrier Proteins; D050961:Glycine Decarboxylase Complex H-Protein; D013763:Tetrahydrofolates; D000643:Ammonium Chloride; C013123:5,10-methylenetetrahydrofolic acid; C030371:5,6,7,8-tetrahydrofolic acid; D000641:Ammonia; D000594:Amino Acid Oxidoreductases; D050841:Glycine Dehydrogenase (Decarboxylating); D014166:Transferases; D019877:Hydroxymethyl and Formyl Transferases; D050960:Aminomethyltransferase