A possible method for estimating hormone effects on enzyme synthesis

Abstract

The activities of four rat liver enzymes (glucose 6-phosphate dehydrogenase, serine dehydrase, glutamic-pyruvic transaminase, and glutamic-oxaloacetic transaminase) were studied in a 90% glucose to 90% casein or a 90% casein to 90% glucose dietary change in the absence and in the presence of exogenous hydrocortisone. From the rates of increases or decreases in enzyme activities the rates of synthesis and values of half-lives of these enzymes were estimated. Comparison of these parameters in the presence and absence of exogenous hydrocortisone indicate that the hormone increases the activity of glucose 6-phosphate dehydrogenase (in the glucose to protein dietary change but not in the reverse dietary change) and glutamic-pyruvic transaminase by increasing the rates of synthesis of these enzymes without altering their rates of degradation. The half-lives of these enzymes were not altered by dietary protein. Serine dehydrase activity was increased by hydrocortisone and it appeared that while protein only increased the rate of synthesis of this enzyme, hydrocortisone increased its half-life and rate of synthesis. The activity of glutamic-oxaloacetic transaminase was increased by dietary protein and also by the hormone. The half-life of the enzyme was smaller in protein-fed or hydrocortisone-treated animals; the hormone apparently mimicking the effect of dietary protein. The utility of the method used for evaluating hormone effects on enzyme activities were discussed with respect to applicability, rapidity, and ease especially in cases when antibody precipitation is not practical.