Proteolytic modification of membrane‐associated phospholipase C‐β by μ‐calpain enhances its activation by G‐protein βγ subunits in human platelets

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