Studies on the Role of 3-Phosphoglycerate Dehydrogenase in the Regulation of Serine Biosynthesis in Rat Liver

The rate of l-serine biosynthesis from 3-phosphoglycerate by rat liver soluble fractions was found to be directly proportional to the activity of 3-P-glycerate dehydrogenase in the extracts. This relationship was observed in rats fed a low protein diet, in rats fed a low protein diet supplemented with 2% methionine, and in rats given intraperitoneal injections of cortisone acetate. The mechanisms of change in hepatic 3-P-glycerate dehydrogenase activity in response to dietary or hormonal influences were evaluated by kinetic analysis of the transition between steady state levels of the enzyme. These dietary and hormonal alterations did not result in large changes in the estimated turnover of hepatic 3-P-glycerate dehydrogenase. The higher enzyme level in rats fed low protein diets was attributed to an 11-fold increase in estimated enzyme synthetic rate. Supplementation of the low protein diet with 2% methionine or cortisone acetate administration reduces the stimulatory effect of the low protein diet on the rate of synthesis of rat liver 3-P-glycerate dehydrogenase.