title: Physical and functional association of cytosolic inositolphospholipid-specific phospholipase C of calf thymocytes with a GTP-binding protein.
abstract: A soluble inositolphospholipid-specific phospholipase C (PI-phospholipase C) has been purified 5,800-fold from the cytosolic fraction of calf thymocytes. The purification was achieved by sequential column chromatographies on DEAE-Sepharose CL-6B, heparin-Sepharose CL-6B, Sephacryl S-300, Mono S, and Superose 12, followed by column chromatography on Sephadex G-100 in the presence of 1% sodium cholate. The enzyme thus purified was found to be homogeneous on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weight of the enzyme was estimated to be 68 kDa by SDS-PAGE. The enzyme is specific for inositol phospholipids. Phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate (PIP2) were hydrolyzed, but phosphatidylcholine and phosphatidylethanolamine were not affected by the enzyme. GTP gamma S-binding activity was detected in the enzyme fractions after all the purification steps, but not in the final enzyme preparation. The PI-phospholipase C and GTP gamma S-binding activities in the partially purified enzyme preparation could be separated by the column chromatography on Sephadex G-100 only in the presence of 1% sodium cholate. Thus, the soluble PI-phospholipase C has affinity to a GTP-binding protein. SDS-PAGE of the GTP-binding fractions eluted from the Sephadex G-100 column gave three visible bands of 54, 41, and 27 kDa polypeptide was specifically ADP-ribosylated by pertussis toxin. Furthermore, it was found that GTP and GTP gamma S (10 microM and 1 mM) could enhance the PIP2 hydrolysis activity of the partially purified enzyme in the presence of 3 mM EGTA, but the purified enzyme after separation from the GTP-binding activity was not affected by GTP and GTP gamma S. The soluble PI-phospholipase C of calf thymocytes may be not only physically but also functionally associated with a GTP-binding protein.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D002845:Chromatography; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D010716:Phosphatidylinositols / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D013873:Thionucleotides / Q000378:metabolism / Q000494:pharmacology; D013950:Thymus Gland / Q000201:enzymology*; D010738:Type C Phospholipases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D010716:Phosphatidylinositols; D011480:Protease Inhibitors; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium