Infulence of hormones and medium composition on the degradation of phosphoenolpyruvate carboxykinase (GTP) and total protein in Reuber H35 cells.

Reuber H35 cells were pulse-labeled with radioactive leucine and the influence of hormones, serum, and amino acids on protein degradation was investigated during a subsequent chase period. Radioactive, immunoprecipitable phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) had a half-life of 5 to 6 hours which was not influenced by either iV',O"-dibutyryl adenosine 3':5'-monophosphate, dexamethasone, or insulin. The rate of phosphoenolpymvate carboxykinase degradation was the same under steady state conditions as during the approach to a new steady state following hormonal induction or deinduction of the enzyme. Therefore, hormonal regulation of enzyme activity in uivo is the result of changes in the rate of enzyme synthesis.