Inhibition of glusoce-5-phosphate-dehydrogenase by dipyridamole. II

Abstract

We have studied the kinetics of the reaction catalized by the glucose-6-phosphate- dehydrogenase, in relation to the variations of the concentrations of substrate and cofactor, in order to get a better knowledge of the mechanism of the inhibitory effect produced by Dipyridamole (DPD) and described in a previous paper (3). It has been seen that the DPD modifies the value of the Hill «n» coefficient, in dependence of the sustrate concentrations, from 1.26 in absence of DPD to 0.94 and 0.80 in presence of DPD 0.1 and 0.5 mM, respectively. It shows that DPD behaves as a competitive inhibitor of the glucose-6-phosphate-deshidrogenase in function of the substrate, and at the same time it causes a change in the apparent order of the reaction.

On the other side, when we have studied the enzymatic kinetics in function of the cofactor, the DPD behaves as an non-competitive inhibitor, without altering the apparent order of the reaction («n» = 1.22 in absence and presence of DPD).