Studies on the kinetic effects of cyclic nucleotides dependent glutamate dehydrogenase

Abstract

Stopped-flow spectrophotometric studies of the reductive amination of L-ketoglutarate by L-glutamate dehydrogenase showed a biphase time course, which consisted of a rapid first phase lasting 60-100 msec and a slow final phase in which the rate of coenzyme oxidation increased until the coenzyme was depleted. The effects of 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) on the time course of both phases were established. The results showed that in the concentration ranges used the cyclic nucleotides accelerate the catalytic reaction. The effect of cAMP was more pronounced as compared to cGMP. In all cases this influence was most clearly expressed in the first phase. Using an Arrhenius plot the activation parameters were calculated. The experiments with cAMP and cGMP at different molar ratios showed that a specific cAMP binding may occur.