title: Purification and characterization of two immunologically distinct phosphoinositide-specific phospholipases C from bovine brain.
abstract: We previously reported (Ryu, S. H., Cho, K. S., Lee, K. Y., Suh, P. G., and Rhee, S. G. (1986) Biochem. Biophys. Res. Commun. 141, 137-144) that cytosolic fractions of bovine brain contain two phosphoinositide-specific phospholipase C (PLC), PLC-I and PLC-II. In this paper purification procedures and properties of these two forms of enzyme are presented. The two enzymes exhibit similar substrate specificity. Both PLC-I and PLC-II catalyze the hydrolysis of phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP2). Yet, they respond differently to activators such as Ca2+ and nucleotides and to inhibitory divalent metal ions such as Hg2+ and Cd2+. In addition, they are immunologically distinct as evidenced by the fact that monoclonal antibodies directed against either enzyme do not cross-react with the other. Their activities are Ca2+ concentration-dependent. PIP and PIP2 are better substrates than PI for both PLC-I and PLC-II when the concentration of Ca2+ is in the micromolar range. Study of the effect of nucleotides, such as GTP, guanosine 5'-(3-O-thio)triphosphate, guanyl-5'-yl imidodiphosphate, and ATP, on the activities of both isozymes with PIP2 as substrate revealed that (i) in the absence of Ca2+, PLC-I activity is enhanced by 400% by either GTP or ATP. In the presence of Ca2+ (a condition in which PLC-I exhibits much higher activity), the activation factor by nucleotides is diminished to approximately 140%. (ii) without Ca2+, PLC-II activity is too low to measure with or without added nucleotides. The effect of nucleotides on PLC-II activity is trivial in the presence of Ca2+. In addition, studies on the effect of metal ions on PI hydrolysis showed that the activities of both PLC-I and PLC-II are not affected by 50 microM of Mg2+, Mn2+, Ca2+, or Ni2+. However, Hg2+, Zn2+, and Cu2+ inhibited both PLC-I and PLC-II, with PLC-II exhibiting much higher sensitivity to these metal ions than PLC-I. For example, the value of I0.5 for Hg2+ inhibition is 0.2 microM for PLC-II and 1 microM for PLC-I. Cd2+ selectively inhibits PLC-II with a I0.5 value of 5 microM. Most of these metal ions' inhibition can be overcome by either dithiothreitol or EDTA.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D001921:Brain / Q000201:enzymology*; D002413:Cations, Divalent / Q000378:metabolism; D002417:Cattle; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D003600:Cytosol / Q000201:enzymology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000276:immunology / Q000302:isolation & purification*; D009711:Nucleotides / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000145:classification / Q000276:immunology / Q000302:isolation & purification*
chemical_list: D000911:Antibodies, Monoclonal; D002413:Cations, Divalent; D007527:Isoenzymes; D009711:Nucleotides; D010716:Phosphatidylinositols; D010738:Type C Phospholipases