Diacylglycerol (DAG), as the second massenger to activate protein kinase C (PKC), may be derived not only from hydrolysis of phos-phatidylinositol (PtdIns), but also from hy-drolysis of phosphatidylcholine (PC) , in which phospholipases of the type C and D (PLC andPLD ) participate . Fatty acids (FA), the pro-ducts of phospholipases A2(PLA2) also acti vates PKC. PKC has at least 10 subspeciesand 3 group, namely classical PKC, new PKC and atypical PKC. PKC also participates inregulation of gene expression.