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 beta and/or gamma subunits. Only AS/1 specifically immunoprecipitated the alpha 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 beta subunit of the guanine nucleotide-binding proteins (Gs and Gi) 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 beta subunit of Gs and Gi.