[On the mechanism of action of glutamate dehydrogenase from pea seedlings and the regulation of the activity by adenosine phosphates, the energy charge and ions]

The mechanism of action and the regulatory properties of glutamate dehydrogenase from pea seedlings (Pisum sativum, var. Späths Violetta) have been investigated by using a highly purified preparation of the enzyme. Kinetic experiments show that the binding of the coenzyme (NAD(+) or NADH) and the substrate (L-glutamate or α-ketoglutarate) is sequential. The formation of a quarternary complex with ammonia as additional substrate is questionable, as can be seen from the kinetic data. The anions of the ammonia source have a strong rate-regulating effect on the NADH reaction. The adenosinphosphates AMP, ADP, and ATP exert an inhibiting effect on both the reductive amination and the oxidative deamination reaction. The former reaction is inhibited half as much as the latter. Dead end inhibition offers a sufficient explanation for this effect. The glutamate dehydrogenase from pea seedlings is not regulated by the energy charge. Zn(2+) ions are strong inhibitors of the NADH-reaction; their inhibitory effect on the activity is indirect and can be reversed by addition of ATP. A reaction sequence is formulated.