A cytosolic protein activator of cardiac sarcolemmal phosphoinositide phospholipase C.
Ca2+ dependent polyphosphoinositide phospholipase C (PLC) activity in cardiac sarcolemma hydrolyzed both endogenous and exogenous phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) with an associated increase in inositol bisphosphate (IP2). Dialyzed cytosol and certain fractions of cytosol isolated by anion exchange or gel filtration chromatography activated sarcolemmal PLC activity by approx. 100%. The PLC activator eluted with an apparent molecular weight of 160 Kdal on a Sephacryl 300 column and was destroyed by heat or trypsin treatment. Exogenous 3H-PIP2 was not hydrolyzed by cytosolic fractions containing sarcolemmal PLC activator. These studies demonstrate that the polyphosphoinositide PLC in cardiac sarcolemma is regulated by a cytosolic protein.
Quist
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Department of Pharmacology, Texas College of Osteopathic Medicine, Fort Worth 76107.
Powell
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D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D004789:Enzyme Activation; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D009124:Muscle Proteins / Q000502:physiology*; D009206:Myocardium / Q000201:enzymology*; D010716:Phosphatidylinositols / Q000378:metabolism*; D012508:Sarcolemma / Q000201:enzymology*; D010738:Type C Phospholipases / Q000378:metabolism*
D007295:Inositol Phosphates; D009124:Muscle Proteins; D010716:Phosphatidylinositols; D010738:Type C Phospholipases; D002118:Calcium