Rapid dephosphorylation of a Mr 80,000 protein, a specific substrate of protein kinase C upon removal of phorbol esters, bombesin and vasopressin.

The mitogens phorbol 12,13-dibutyrate, bombesin and vasopressin stimulate the phosphorylation of an acidic Mr 80,000 cellular protein, a specific substrate of protein kinase C, in intact Swiss 3T3 cells. Phosphorylation of this substrate was rapidly reversed upon the removal of each of these agents. Dephosphorylation occurred with a similar half-life in each of the cases studied (2.2, 1.5 and 2 minutes for phorbol 12,13-dibutyrate, bombesin and vasopressin respectively) and agreed closely with the dissociation of the ligands from their specific high-affinity binding sites in Swiss 3T3 cells.