title: Purification and characterization of G proteins from human brain: modification of GTPase activity upon phosphorylation.
abstract: Three G proteins from human brain membranes were purified to near homogeneity by conventional techniques including preparative electrophoresis. These G proteins were characterized by their ability to bind GTP, GDP and GTP analogs. Two of these proteins have molecular weights of 50,000 (G50) and 36,000 (G36), as determined on SDS-gels. G36 was ADP-ribosylated by pertussis toxin. Thus, G50 could represent a Gs alpha subunit, whereas G36 could be Gi alpha or Go alpha. G50 was phosphorylated by cAMP dependent protein kinase and protein kinase C. G36 was phosphorylated by a protein kinase independent of calcium and phospholipid, a proteolytic product of protein kinase C, analogous to protein kinase M. Phosphorylation of G36 by this protein kinase induced a dramatic decrease in its GTPase activity. The third G protein, of molecular weight 22,000 probably belongs to the group of monomeric G proteins possessing functional similarities with ras gene products. The regulation of G proteins involving calcium-dependent and independent pathways is delineated.
authors.affiliation: Centre de Recherche Delalande, Rueil-Malmaison, France.
authors.forename: C
authors.initials: C
authors.lastname: Sauvage
authors.forename: J F
authors.initials: JF
authors.lastname: Rumigny
authors.forename: M
authors.initials: M
authors.lastname: Maitre
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D001921:Brain / Q000201:enzymology*; D003429:Cross Reactions; D020558:GTP Phosphohydrolases / Q000187:drug effects / Q000302:isolation & purification* / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000276:immunology / Q000302:isolation & purification* / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D008970:Molecular Weight; D037342:Pertussis Toxin; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D016283:Proto-Oncogene Proteins p21(ras) / Q000276:immunology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D011494:Protein Kinases; D011493:Protein Kinase C; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)