Purification of GTP-binding proteins from bovine brain membranes: Identification of heterogeneity of the α-subunit of G o proteins

Abstract

Using high-resolution Mono Q column chromatography, we purified 6 distinct peaks of GTP-binding proteins from bovine brain membranes. Five of them consisted of 3 polypeptides with αβγ-subunits and served as the substrate of islet-activating protein (IAP), pertussis toxin. The other one was purified as α-subunit alone and was also ADP-ribosylated by IAP in the presence of βγ-subunits. When each α-subunit was characterized by immunoblot analysis using various antibodies with defined specificity, the two of them were identified as g i-1 and G i-2, and other 4 appeared to be G o or G o-like G proteins. The α-subunits of immunologically G o-like proteins were apparently distinguishable from one another on elution profiles from the Mono Q column. Thus, there was a heterogeneity of the α-subunit of G o in the brain membranes. ADP-ribosylation; GTP-binding protein; Islet-activating protein