Protein kinase C negatively modulated by phorbol ester

Abstract

Pretreatment of protein kinase C with 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) and phospholipid resulted in complete inhibition of ATP/phosphotransferase activity, irreversibly. The inactivation by TPA required the phospholipid, and TPA alone did not cause inactivation. Ca²⁺ and diacylglycerol mimicked TPA. This action of TPA was not general for all protein kinases as it did not accelerate the inactivation of the catalytic subunit of cAMP‐dependent protein kinase by phospholipid. The addition of MgATP to the reaction mixture completely protected protein kinase C from being inactivated by TPA, in the presence of phospholipid. The nucleotide‐binding site of the enzyme was probably influenced by the binding of TPA and phospholipid.