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

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Abstract
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.