Human hypoxanthine-guanine phosphoribosyltransferase. IMP-GMP exchange stoichiometry and steady state kinetics of the reaction.

Steady state kinetics of hypoxanthine guanine phosphoribosyltransferase-catalyzed reactions are studied. The results obtained suggest that IMP, GMP, P-Rib-PP, and pyrophosphate bind to the same enzyme form, while hypoxanthine and guanine bind to a different form. Guanine activates IMP-pyrophosphorolysis. During the reaction guanine and IMP are consumed with formation of GM