Antibodies against a retinal guanine nucleotide-binding protein cross-react with a single plasma membrane protein in non-retinal tissues

Antisera (AS/1-AS/6) to purified bovine retinal transducin, a guanine nucleotide-binding protein, were produced in 6 rabbits. Immunoblots showed that the antisera varied in their reactivity with the subunits of transducin; AS/1 reacted strongly with all 3 subunits, while the others reacted with only the β and/or γ subunits. Only AS/1 specifically immunoprecipitated the α subunit radiolabeled with non-covalently bound guanine nucleotides. Immunostaining of plasma membrane proteins from non-retinal tissues with AS-1 revealed a single protein (approx. 35 kDa), most likely representing the β subunit of the guanine nucleotide-binding proteins (G_s and g_i associated with adenylate cyclase. Cerebral cortex showed the highest content of this protein. Antisera against transducin provide a highly specific and sensitive probe for quantitation of the β subunit of G_s and G_i.