Phospholipase C in rat liver plasma membranes. Phosphoinositide specificity and regulation by guanine nucleotides and calcium.
Phospholipase C activity against phosphoinositides in isolated rat liver plasma membranes has been examined using exogenous substrates. The enzyme hydrolyzed phosphatidylinositol 4,5-bisphosphate 30-40-times faster than phosphatidylinositol 4-monophosphate, while phosphatidylinositol was not a substrate. Maximum activity was observed with 1.1 mM phosphatidylinositol 4,5-bisphosphate at pH 5.0. The enzyme was stimulated by micromolar concentrations of Ca2+. The GTP analogue guanylyl (beta,gamma-methylene)diphosphonate enhanced phospholipase C activity at and above 0.3 microM Ca2+, but was inhibitory at 0.1 microM Ca2+. This supports the suggestion that plasma membrane phospholipase C is regulated by guanine nucleotide-binding protein, but indicates a regulatory mechanism different from that of other enzymes regulated by such proteins.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology; D006150:Guanine Nucleotides / Q000494:pharmacology*; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology*; D008297:Male; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000032:analysis*
D006150:Guanine Nucleotides; D010716:Phosphatidylinositols; D010738:Type C Phospholipases; D002118:Calcium