REGULATION OF PHOSPHOLIPASE C-BETA ISOZYMES BY G-PROTEINS

Phospholipase C (PLC) isozymes ave known to be regulated in part, by h eterotrimeric GTP-binding protein (G-protein) subunits, including G al pha subunits of the G(q) family and G beta gamma subunits. New data sh ow that PLC can also be regulated by a high molecular weight G-protein that doubles as a cellular transglutaminase. Furthermore, a soluble p hosphatidylinositol transfer protein (PITP) has been implicated in sus taining the activity of PLC by delivering substrate to the plasma memb rane. Such diverse regulatory mechanisms imply that the PLC isozymes a re precisely controlled and have specific roles in generating second m essengers in response to various external stimuli.