Diglyceride

Abstract: Inositol phospholipids have attracted great attention from researchers studying the activation of cellular functions and proliferation. In the action of a group of hormones, neurotransmitters, or other biologically active substances, including some growth factors, a signal-induced degradation of the phospholipids may generate important intracellular second messengers that function differently from cyclic AMP. The response of inositol phospholipids to the activation of cell surface receptors was first recognized by Hokin & Hokin ( 1953), who showed with pancreatic slices that ace­ tylcholine induces a rapid incorporation of 32p into phosphatidylinositol (PI) and phosphatidic acid. It later became evident that breakdown and resynthesis of inositol phospholipids occur in many cell types in response

Abstract: Many lipids or lipid-derived products generated by phospholipases acting on phospholipids in membranes are implicated as mediators and second messengers in signal transduction. Our current understanding of the primary sequence relationships within the class of extracellular phospholipase A2's and among the numerous forms of the mammalian phosphatidylinositol-specific phospholipase C's is reviewed. New results suggesting roles for these phospholipases as well as other phospholipases such as phospholipase C and D acting on phosphatidlycholine in generating arachidonic acid for eicosanoid biosynthesis, inositol phosphates for Ca2+ mobilization, and diglyceride for protein kinase C activation through receptor-mediated processes, are discussed. In addition, the possible role of phospholipases acting on sphingolipids such as sphinglomyelinase in generating lipid mediators is considered.