Gierschik, P., Metabolic Diseases Branch, National Institute of Arthritis, Diabetes, Digestive, and Kidney Diseases, Bethesda, MD 20892, United States
Milligan, G., Metabolic Diseases Branch, National Institute of Arthritis, Diabetes, Digestive, and Kidney Diseases, Bethesda, MD 20892, United States
Pines, M., Metabolic Diseases Branch, National Institute of Arthritis, Diabetes, Digestive, and Kidney Diseases, Bethesda, MD 20892, United States
Goldsmith, P.
Codina, J.
Klee, W.
Spiegel, A.

We immunized rabbits with purified guanine nucleotide-binding proteins (G proteins) from bovine brain and obtained an antiserum, RV3, that reacts specifically with the α subunit (39 kDa) of a G protein of unknown function, termed G(o), as well as with the β subunit (35 kDa) common to all G proteins. RV3 showed no crossreactivity with the α subunits of the stimulatory (G(s) or inhibitory (G(i)) G proteins associated with adenylate cyclase, nor with that of the rod outer segment G protein, transducin. Immunoblots with crude and affinity-purified antiserum showed that RV3 specifically recognizes the G(o) α subunit and the β subunit in crude brain membranes. Using RV3, we found approximately equal amounts of G(o) in brain membranes from frog, chicken, rat, cow, and man. Quantitative immunoblotting gave G(o) α subunit/β subunit ratios ~ 1 in cerebral cortex, raising the possibility that free G(o) α subunit (unassociated with β subunit) may exist in brain. The concentration of G(o) α subunit in cerebral cortex is about 5 times that of G(i) α subunit. The results show that G(o) is an immunochemically distinct, highly conserved protein distributed throughout the brain, with particularly high concentrations in forebrain.