Human hypoxanthine-guanine phosphoribosyltransferase. Steady state kinetics of the forward and reverse reactions.

A steady state kinetic study of the hypoxanthine-guanine phosphoribosyltransferase-catalyzed reaction in the forward and the reverse directions was carried out. The results obtained favor a sequential mechanism where the monomagnesium complexes of IMP and PPi bind to the enzyme in a rapid equilibrium random fashion while products must dissociate from the enzyme in ordered sequence, first the purine base and then the magnesium complex(es) of P-Rib-PP.