Influence of Turnover Rates on the Responses of Enzymes to Cortisone

Abstract

Cortisone administration over a period of 4 days results in increased enzyme activity of rat liver tryptophan pyrrolase, tyrosine-glutamic transaminase, glutamic-alanine transaminase, and arginase. These enzymes differed greatly in turnover rates: from tyrosine-glutamic transaminase with a half-life of 2.0 hr to arginase with a half-life of 4 days. Tryptophan pyrrolase and tyrosine-glutamic transaminase appear to respond rapidly to cortisone whereas glutamic-alanine transaminase and arginase respond more slowly. Although the time course and magnitude of responses are quite different among the four enzymes, the ratios of rates of synthesis under basal conditions to rates of synthesis in cortisone treated animals are quite similar. Thus the apparent small response of arginase and the slow response of glutamic-alanine transaminase as compared to the rapid and large response of tryptophan pyrrolase and tyrosine-glutamic transaminase are not a reflection of low sensitivity to the effects of cortisone, but of the slower turnover of these enzymes.