Regulation of phospholipase C-beta isozymes by G-proteins.

Phospholipase C (PLC) isozymes are known to be regulated, in part, by heterotrimeric GTP-binding protein (G-protein) subunits, including Galpha subunits of the G(q) family and Gbetagamma subunits. New data show that PLC can also be regulated by a high molecular weight G-protein that doubles as a cellular transglutaminase. Furthermore, a soluble phosphatidylinositol transfer protein (PITP) has been implicated in sustaining the activity of PLC by delivering substrate to the plasma membrane. Such diverse regulatory mechanisms imply that the PLC isozymes are precisely controlled and have specific roles in generating second messengers in response to various external stimuli.