Human placental glutamate dehydrogenase. Purification--kinetic and regulatory properties--physicochemical studies.

Glutamate dehydrogenase (EC. 1.4.1.3) has been purified more than 9,000 times from human placental alcoholic subfractions as a homogenous protein of 55,155 daltons (subunit molecular weight). Kinetic constants for the reverse reaction (reductive amination of alpha-ketoglutarate) have been shown to be similar to those of the bovine liver enzyme, while the kinetic constants for the forward reaction were markedly different as well as some regulatory properties (lack of activation by ADP in the reverse reaction). The amino acid composition differs from the bovine liver enzyme composition. Furthermore, the tryptic peptide patterns of the placental enzyme and the human liver enzyme have been compared. Besides the low specific activity of this enzyme, the results indicate that human placental glutamate dehydrogenase is closely related to other mammalian glutamate dehydrogenases.