title: Stimulation of ras GTPase activity by an anti-ras monoclonal antibody.
abstract: Wild-type ras has GTPase activity, and this activity is accelerated substantially by GTPase-activating proteins (GAPs). Oncogenic ras species have an abnormally low intrinsic GTPase activity, and this activity is insensitive to GAPs. We confirmed that the anti-ras monoclonal antibody Y13-238 inhibited GAP activity in vitro, but we also noted that this antibody had GAP activity of its own. We studied the GAP activity of Y13-238 in circumstances in which ras GTPase activity was influenced by the GTPase-inhibitory antibody Y13-259 or by substitutions in ras. The GTPase-inhibitory antibody Y13-259 blocked the GAP associated with Y13-238. A ras species with a substitution in the effector loop that blocked conventional GAP activity was sensitive to stimulation by Y13-238. Both Y13-238 and Y13-259 stimulated the autophosphorylation of Ala59Thr ras. We interpreted these data in terms of a model in which the extrinsic factors influence the ras GTPase reaction by affecting the balance between "committed" and "uncommitted" states. We suggest that there is a mechanism distinct from that exploited by conventional GAPs for stimulating ras GTPase activity.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Agellon
authors.forename: J C
authors.initials: JC
authors.lastname: Stone
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D000937:Antigen-Antibody Reactions; D020558:GTP Phosphohydrolases / Q000276:immunology* / Q000378:metabolism; D020690:GTPase-Activating Proteins; D010766:Phosphorylation; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000276:immunology* / Q000378:metabolism; D011994:Recombinant Proteins; D013329:Structure-Activity Relationship; D020703:ras GTPase-Activating Proteins
chemical_list: D000911:Antibodies, Monoclonal; D020690:GTPase-Activating Proteins; D011506:Proteins; D011994:Recombinant Proteins; D020703:ras GTPase-Activating Proteins; D020558:GTP Phosphohydrolases; D016283:Proto-Oncogene Proteins p21(ras)