title: Properties of a novel GTP-binding protein which is associated with soluble phosphoinositides-specific phospholipase C.
abstract: Recently we demonstrated the presence in calf thymocytes of a GTP-binding protein (G-protein) composed of three polypeptides, 54, 41, and 27 kDa, which was physically and functionally associated with a soluble phosphoinositides-specific phospholipase C (PI-phospholipase C). The properties of this G protein were further investigated with the following results. 1) In addition to the ability to bind [35S]guanosine-5'-[gamma-thio]triphosphate (GTP gamma S), the G-protein exhibited GTPase activity, which was enhanced by Mg2+, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol, but inhibited by sodium cholate, GTP gamma S and F-.2) The 54-kDa polypeptide was ADP-ribosylated by pertussis toxin and also by endogenous membrane-bound ADP-ribosyltransferase, but none of these three polypeptides was ADP-ribosylated by cholera toxin. 3) The G-protein did not cross-react with either anti-rat brain alpha 1 (alpha-subunit of inhibitory G-protein, G1), alpha 0 (alpha-subunit of other G1-like G-protein, G0) or beta gamma antibodies. 4) Incubation of this G Protein with GTP gamma S caused dissociation of the three polypeptides. 5) The 27 kDa polypeptide showed GTP-binding activity and enhanced the phosphatidylinositol 4,5-bisphosphate hydrolysis by purified PI-phospholipase C. These results suggest that the PI-phospholipase C-associated G-protein in calf thymocytes may be a novel one and that it is involved in the regulation of PI-phospholipase C activity.
authors.affiliation: Division of Chemical Toxicology and Immunochemistry, Faculty of Pharmaceutical Sciences, University of Tokyo.
authors.forename: P
authors.initials: P
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Toyoshima
authors.forename: T
authors.initials: T
authors.lastname: Osawa
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D002417:Cattle; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008970:Molecular Weight; D010716:Phosphatidylinositols; D013379:Substrate Specificity; D013873:Thionucleotides / Q000378:metabolism; D013950:Thymus Gland / Q000201:enzymology; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D010716:Phosphatidylinositols; D013873:Thionucleotides; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins