G protein-dependent regulation of phospholipase C.

A wide variety of receptors for hormones, neurotransmitters and growth factors control cell function via the GTP-dependent activation of phosphoinositide specific phospholipase C (PIC). At least two distinct GTP dependent proteins (G proteins) have been implicated in coupling different receptor populations to the activation of PIC and five immunologically distinct isozymes of PIC have been purified to homogeneity, prompting speculation about the potential for multiple modes of organization of the participants in this signal transduction pathway. The mechanism of hormone and G protein-dependent regulation of PIC has been studied in detail using [3H]inositol labelled turkey erythrocyte membranes and these experiments have provided strong support for the involvement of a heterotrimeric G protein. Further progress requires the development of reconstitution assays in which the regulation of isolated PICs by defined G proteins can be demonstrated.