APPLICATION OF SYNTHETIC PEPTIDES AS SUBSTRATES FOR REVERSIBLE PHOSPHORYLATION

Two highly homologous synthetic peptides MLC(3-13) (K-R-A-K-A-K-T-T-K-K-R-G) and MLC(5-13) (A-K-A-K-T-T-K-K-R-G) corresponding to the amino terminal amino acid sequence of smooth muscle myosin light chain were utilized as substrates for protein kinase C purified from murine lymphosarcoma tumors to determine the role of the primary amino acid sequence of protein kinase C substrates in defining the lipid (phosphatidyl serine and diacylglycerol) requirements for the activation of the enzyme. Removal of the basic residues lysine and arginine from the amino terminus of MLC(3-13) did not have a significant effect on the Ka value of diacylglycerol. The binding of effector to calcium-protein kinase C appears to be random since binding of one effector did not block the binding of the other. MLC(3-13) phosphorylated by protein Kinase C and an S6-21, a synthetic peptide corresponding to the carbo>fy terminus of the ribosomal protein S6 and phosphorylated by an S6/H4 for the catalytic subunits of phosphoprotein p|