Two alpha subunits of the Gq class of G proteins stimulate phosphoinositide phospholipase C-beta 1 activity

Two G protein alpha subunits were detected in preparations of GTP gamma S-dependent, phosphoinositide-specific phospholipase C-activating proteins from bovine liver membranes. Partial resolution of the two alpha subunits, of molecular mass 42 and 43 kDa, was achieved by Mono Q chromatography. Quantitation of the levels of each alpha subunit and reconstitution assays demonstrated that each possessed stimulatory activity towards the beta 1 isozyme of phospholipase C. Immunoblot analysis showed that the 42 kDa protein was immunologically related to alpha q, whereas the 43 kDa protein was related to alpha 11, another member of the Gq class. The data thus show that two different alpha subunits of the Gq class of G proteins stimulate phospholipase C-beta 1 Activity.