Glucocorticoids and Transaminase Activity VI. COMPARISON OF THE ADAPTIVE INCREASES OF ALANINE- AND TYROSINE-(Y-KETOGLUTARATE TRANSAMINASES*

The activity of alanine-cr-ketoglutarate transaminase (n-alanine :2-oxoglutarate aminotransferase, EC 2.6.1.2) is increased markedly in the livers of diabetic or fasted rats (1). The induction of this enzyme also occurs when either intact or adrenalectomized rats are fed diets high in protein or given corticosteroid injections (24). The adaptive response of this enzyme in glucocorticoid-sensitive tissues, such as thymus (4) and Walker carcinoma 256 (5), is of particular interest since most studies of adaptive enzymes have been restricted to liver. Lin and Knox (6) and Sereni, Kenney, and Kretchmer (7) have shown that tyrosine-cr-ketoglutarate transaminase (n-tyrosine : 2-oxoglutarate aminotransferase, EC 2.6.1.5) is increased several fold in the livers of rats treated by injection with cortisol. Before undertaking studies directed toward an understanding of the mechanism of enzyme induction and the physiological significance of the altered activity of these enzymes, further information on the comparative responses of alanine and tyrosine transaminases seemed desirable. The present report describes a comparative study of these two transaminases with special reference to (a) the time course of the response after the injection of cortisol, (5) induction by substrates, (c) effects of adrenalectomy on the endogenous and cortisol-induced levels, (d) effects of fasting, high protein diets, and alloxan diabetes, and (e) their response in cortisol-sensitive tissues. Differences in the specificity and nature of induction of these two adaptive enzymes were noted. A preliminary report of certain aspects of this work has appeared (8).