Pyrimidine nucleoside monophosphate kinase from rat bone marrow cells: a kinetic analysis of the reaction mechanism.

A kinetic analysis of the reaction mechanism of pyrimidine nucleoside monophosphate kinase was carried out with a highly purified enzyme preparation from rat bone marrow cells. The results of initial rate and product inhibition studies provided insight into the mode of action of the enzyme. The data support the views that the reaction mechanism is sequential and nonequilibrium in nature. Substrates bind to the enzyme in a random order. Substrate binding is cooperative. That is, the binding of the first substrate facilitates the binding of the second substrate. UMP can bind to the purine site on the enzyme, resulting in substrate inhibition. Product inhibition can result from the binding of UDP to either the pyrimidine or purine site, or from the binding of ADP to the purine site.