STEROID HORMONE ACTIVATION OF L-ALANINE OXIDATION CATALYZED BY A SUBUNIT OF CRYSTALLINE GLUTAMIC DEHYDROGENASE

Abstract

The ability of crystalline glutamic dehydrogenase of beef liver to catalyze the reversible oxidative deamination of L-alanine has been studied. Certain steroid hormones and diethylstilbestrol, 1, 10-phenanthroline, and high pH, all of which promote disaggregation of the protein into subunits, stimulate the alanine and inhibit the glutamic dehydrogenase reactions. ADP, DPN, and TPN, which cause association of the enzyme, inhibit alanine and stimulate glutamic dehydrogenase. It appears that the associated form of the enzyme (molecular weight 1,000,000) is principally concerned with the glutamic dehydrogenase reaction. A subunit catalyzes primarily the alanine-pyruvate interconversion. These findings suggest a means by which steroid hormones by changing the physical properties of an enzyme can alter both its kinetic properties and its substrate specificity.