Regulation of bovine glutamate dehydrogenase. The effects of pH and ADP

The activity of bovine liver glutamate dehydrogenase is affected in several ways depending on substrate concentrations and pH. At ph 6.5 and below, both oxidative deamination and reductive amination reactions are inhibited by ADP. At pH 7.0 and above both activatory and inhibitory effects can be observed depending on substrate concentrations. The effects are explicable in terms of a model with ADP binding at both a regulatory site and competing with coenzyme at the active site. The activatory effects of ADP result from destabilization of various abortive complexes by ADP binding to its regulatory site. The concerted effects of pH and ADP lead to a potentiation of either activation effects or inhibition effects depending on conditions. A consideration of in vivo concentrations of the various substrates involved and intramitochondrial pH and adenine nucleotide levels suggests that in vivo the reductive amination reaction is favored. It is suggested that glutamate dehydrogenase may be intimately involved with regulation of the urea cycle by responding to changes in the mitochondrial ammonia levels.