Small Molecular Weight GTP-binding Proteins in Human Platelet Membranes: Purification and characterization of a novel GTP-binding protein with a molecular weight of 22,000

摘要: When guanosine 5'-(3-O-[35S]thio)triphosphate (GTP gamma S)-binding activity was assayed in the particulate and cytosol fractions of human platelets, most found fraction. GTP-binding proteins (G proteins) were extracted from fraction by sodium cholate purified several column chromatographies. At least three G with Mr values about 21,000, 22,000, 24,000 (21K G, 22K 24K respectively) separated addition to stimulatory (Gs) inhibitory (Gi) regulatory adenylate cyclase. Among them, amount more than 10-fold those other proteins. near homogeneity characterized. specifically bound GTP S, GTP, GDP, a Kd value for S 50 nM. [35S]GTP binding inhibited pretreatment N-ethylmaleimide. hydrolyzed liberate Pi, turnover number 0.01 min-1. not copurified beta subunits Gs Gi recognized antibodies against ADP-ribosylation factor ras protein. The peptide map different smg-25A rho proteins, which we have bovine brain membranes. 21K identified be c-ras protein, but unidentified. These results indicate that there are multiple platelet membranes novel protein (22K G) is major platelets.