Antisera against a guanine nucleotide binding protein from retina cross-react with the β subunit of the adenyl cyclase-associated guanine nucleotide binding proteins, N(s) and N(i)

Antisera were produced in rabbits against a guanine nucleotide binding protein (N protein), transducin, purified from bovine retina. Antiserum AS/1, which recognized all three subunits (α, β, and γ) of the holoprotein, was tested for cross-reactivity with the subunits of the adenylyl cyclase [adenylate cyclase; ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1]-associated stimulatory (N(s)) and inhibitory (N(i)) N proteins purified from human erythrocytes. AS/1 showed strong reactivity against the β subunits of both N(s) and N(i) but failed to cross-react with either the α or γ subunits of N(s) and N(i). Seven additional antisera against transducin reacted with the β subunits but not with the α or γ subunits of N(s) and N(i). A single antiserum against transducin reacted with the α subunit of N(i) but not of N(s). Immunostaining of the β subunits of N(s) and N(i) was proportional to the amount of β subunit blotted and to the antiserum concentration. Immunostaining of either human erythrocyte or bovine cerebral cortical plasma membrane proteins with AS/1 showed a single band, comigrating with the β subunit of transducin; this band was absent in bovine erythrocyte membranes. Estimation of the amount of β subunit by immunoblotting with AS/1 showed that the β subunit comprises ≃ 2% of bovine cerebral cortical plasma membrane protein, ≃ 100-fold more than in human erythrocyte membranes. These findings provide immunochemical evidence for similarities in the β subunits and differences in the α and γ subunits of this family of N proteins. Antisera against transducin react specifically with the β subunits of N(s) and N(i) in crude plasma membranes and, thus, can serve as specific probes for the β subunit.