Stimulation by glucagon and adenosine-3',5'-cyclic monophosphate of protein degradation in Reuber H35 hepatoma monolayers.

Protein degradation in Reuber H35 hepatoma monolayers was measured as release of radioactive trichloroacetic acid-soluble material from intracellular protein labelled with [3H]leucine for 16 hr followed by 3-hr chase period. Proteolysis in this system was stimulated by physiological concentration of glucagon reaching a maximum at 10(-7) M with an increase of 30%. Dibutyryl cyclic AMP also had a stimulatory effect. When both glucagon and dibutyryl cyclic AMP were present at optimal concentrations, their effects were not additive suggesting that glucagon may act via the formation of cyclic AMP. In the presence of protein synthesis inhibitor, cycloheximide or puromycin, proteolysis remained responsive to glucagon. Glucagon counteracted the inhibitory effect of insulin on proteolysis.