PHOSPHORYLATION OF MARCKS, NEUROMODULIN, AND NEUROGRANIN BY PROTEIN-KINASE-C EXHIBITS DIFFERENTIAL RESPONSES TO DIACYLGLYCEROLS

Diacylglycerols (DG) derived from brain phosphatidylinositol (PI) and phosphatidylcholine (PC) and synthetic 1,2-dioleoylglycerol (diC(18:1) ) and 1,2-dioctanoylglycerol (diC(8)) were tested for their efficacy i n stimulating PKC-catalyzed phosphorylation of three physiological sub strates in the brain, namely, MARCKS, neuromodulin (Nm), and neurogran in (Ng). The A(0.5) of these DGs for PKC were variable dependent on th e protein substrates; the values were lowest with MARCKS and highest w ith Ng. With Ng as a substrate the A(0.5) of these DGs for PKC gamma w ere PI- and PC-DGs < diC(18:1) < diC(8). Both PI- and PC-DGs, in spite of their differences in unsaturated fatty acids content, were similar ly effective in stimulating PKC. Since the phosphorylation of MARCKS, as compared to those of Nm and Ng, has the lowest A(0.5) With the vari ous DGs, it seems that among these three PKC substrates MARCKS is most readily phosphorylated by PKCs following DG formation in vivo.