The purification and physical properties of glutamate dehydrogenase from rat liver.

Glutamate dehydrogenase has been purified and crystallized from rat liver mitochondria and from whole rat liver preparations. No differences in the enzyme prepared by the two different methods have been observed and there is no evidence that more than one glutamate dehydrogenase occurs in rat liver. The pure enzyme has a molecular weight of 350,000 f 20,000 and consists of six to eight subunits. In contrast to the bovine liver enzyme, rat liver glutamate dehydrogenase does not polymerize to higher molecular weight forms as the enzyme concentration is raised, even in the presence of nucleotides which promote the association of the bovine liver enzyme. Also in contrast to the bovine liver enzyme, the rat liver glutamate dehydrogenase is rather unstable during the assay at low enzyme concentrations. The amino acid composition and peptide maps of the rat and bovine liver enzymes are quite similar, indicating only a few amino acid replacements. The fact that the polymerization of the bovine liver enzyme may be important in the regulation of activity by purine nucleotides in vivo indicates that the rat liver enzyme must differ with respect to such control since polymerization is lacking.