Regulation of Polyphosphoinositide-specific Phospholipase C Activity by Purified G q

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Abstract
The hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP 2 ) by phospholipase C yields the second messengers inositol 1,4,5-trisphosphate (InsP 3 ) and 1,2-diacylglycerol. This activity is regulated by a variety of hormones through G protein pathways. However, the specific G protein or proteins involved has not been identified. The α subunit of a newly discovered pertussis toxin-insensitive G protein (G q ) has recently been isolated and is now shown to stimulate the activity of polyphosphoinositide-specific phospholipase C (PI-PLC) from bovine brain. Both the maximal activity and the affinity of PI-PLC for calcium ion were affected. These results identify G q as a G protein that regulates PI-PLC.