The role of calcium, diglyceride ester bindings and a synthetic polypeptide in protein kinase C activation

Protein kinase C, which plays a significant role in the polyphosphoinositide pathway of transmembrane signaling, is activated by a large class of extracellular ligands including neurotransmitters, hormones and growth factors. Diacylglycerols are the intracellular mediators of protein kinase C activation. Tumor promoting phorbol esters mimic the diacylglycerol action in binding to the same site. Active diacylglycerols have the 1.2 sn configuration and saturated short chain or unsaturated long chain fatty acids. Alkyl analogs of diacylglycerols were devoid of activity when an ether bond was present in position 1, whereas activity of the alkyl analog in position 2 was retained. Protein kinase C activation and 3H-TPA binding to the enzyme occurred in the presence of 0.5 mM EGTA. Moreover it has been shown in vivo that full activation of the enzyme was obtained in the intact platelets loaded with an excess of Quin 2, prior to stimulation by phorbol esters. A peptide (residues 499-513) was synthesized which enhanced the affinity of protein kinase C for histone. It is suggested that it may be the receptor site for another peptide of the enzyme (residues 19 to 36) which behaves as a pseudosubstrate.