Proteolytic modification of membrane-associated phospholipase C-beta by mu-calpain enhances its activation by G-protein beta gamma subunits in human platelets.

Membrane-associated phosphoinositide-phospholipase C (PI-PLC)-beta (150 kDa) and its truncated forms (100 kDa and 45 kDa) were purified from human platelets. The 100 kDa PI-PLC-beta was found to be activated to a greater extent by brain G-protein beta gamma subunits compared to the intact 150 kDa enzyme. Furthermore, treatment with mu-calpain of the intact PI-PLC-beta (150 kDa) caused a marked augmentation of its activation by beta gamma subunits. This enhanced PLC activation by beta gamma subunits was due to truncation by mu-calpain, producing a 100 kDa PI-PLC, but not by another protease, thrombin.