Phosphorylation of a 16-kDa protein by diacylglycerol-activated protein kinase C in vitro and by vasopressin in intact hepatocytes.

A 16-kDa protein present in a purified rat liver plasma membrane fraction and also in cytosol can be phosphorylated by endogenous diacylglycerol-activated protein kinase C. In intact hepatocytes prelabeled with 32P, vasopressin causes a rapid increase in the phosphorylation of a 16-kDa protein having a similar pI value to that observed in in vitro studies. These findings suggest that vasopressin-induced phosphorylation of the 16-kDa in the intact hepatocyte may reflect increased activity of protein kinase C, secondary to membrane polyphosphoinositide breakdown. Phosphorylation of the 16-kDa protein may thus be part of the coordinated mechanism associated with hormonal regulation of cellular Ca2+ fluxes.