Transaminase of Branched Chain Amino Acids

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Abstract
The specific transaminase for leucine (enzyme II) in rat liver was induced very rapidly by administration of cortisol or a high protein diet and the effects of these treatments were additive. Hypophysectomy prolonged the time for full induction of enzyme II by cortisol, while administration of growth hormone inhibited induction of enzyme II completely. Induction of enzyme II by a high protein diet was not influenced by either hypophysectomy or injection of growth hormone. None of these treatments caused any significant change of activity of another isozyme (enzyme I) found in the liver, which was equally active with valine, leucine and isoleucine. Of the isozymes of branched chain amino acid transaminase [EC 2.6.1.6] rat kidney contained only enzyme I and this enzyme was induced by continuous administration of cortisol for several days. Hypophysectomy alone induced kidney enzyme I. Adrenalectomy resulted in decrease in the activities of enzyme II in the liver and enzyme I in the kidney to half the levels in normal rats. Treatment of adrenalectomized rats with insulin or glucagon did not affect enzyme II activity. These results suggest that the isozymes of branched chain amino acid transaminase are under the control of glucocorticoid and that enzyme I has a longer half life than enzyme II. The results also suggest that the amino acid pool in the liver is also involved in induction of enzyme II.

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