title: GTP-binding proteins associated with the human placental syncytiotrophoblast plasma membrane.
abstract: The nature of GTP-binding components associated with isolated human term placental syncytiotrophoblast microvillous plasma membrane vesicles (SPMV) was determined; these are relevant to elucidation of intracellular signal transduction mechanisms. Four proteins were identified, with molecular weights of 29, 27, 23 and 21 kDa, which specifically bound [alpha-32P]GTP in the presence of Mg2+. Studies employing anti-p21c-ras monoclonal antibodies indicated these four GTP-binding components were ras-related and one, the 21 kDa component, may be p21c-ras. In addition, SPMV were also found to express the alpha subunits of three separate G proteins. A 45 kDa SPMV GTP-binding protein was identified as a substrate for Vibrio cholera toxin and was recognized by a rabbit antibody to the alpha subunit of the adenylate cyclase stimulating G protein, Gs. A 41 kDa SPMV GTP-binding protein substrate of Bordetella pertussis toxin was also recognized by rabbit antibodies to the alpha subunits of the adenylate cyclase inhibiting G proteins, Gi-1 and Gi-3. No evidence was found to support the presence of the 21 kDa Gp, a G protein previously associated with membranes prepared from whole placental tissue homogenates.
authors.affiliation: Department of Immunology, University of Liverpool, UK.
authors.forename: P
authors.initials: P
authors.lastname: Kenton
authors.forename: P M
authors.initials: PM
authors.lastname: Johnson
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000911:Antibodies, Monoclonal; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D002824:Chorionic Villi / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D004815:Epidermal Growth Factor / Q000502:physiology; D005260:Female; D019204:GTP-Binding Proteins / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008970:Molecular Weight; D010920:Placenta / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D011233:Precipitin Tests; D011247:Pregnancy; D015398:Signal Transduction / Q000502:physiology; D014327:Trophoblasts / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D000911:Antibodies, Monoclonal; D004815:Epidermal Growth Factor; D000469:Alkaline Phosphatase; D019204:GTP-Binding Proteins