Abstract
Five different pertussis-toxin-sensitive guanine-nucleotide-binding proteins (G proteins) were purified from bovine brain. Immunochemical characterization of .alpha. subunits identified two G.alpha.O proteins (G.alpha.o-I and G.alpha.o-II), two 41-kDa G.alpha.i proteins (G.alpha.i-I and G.alpha.i-II) and the 40-kDa G.alpha.i2 protein. Site-directed antisera specific for G.alpha.o proteins did not differentiate between G.alpha.o-I and G.alpha.o-II. However, in situ peptide mapping using polyacrylamide gel electrophoresis revealed distinct cleavage products with different proteases for each of these proteins. Additionally comparison of Rf values demonstrated a slightly faster migration for G.alpha.o-II than for G.alpha.o-I, which is the only type of G.alpha.o protein present in cell membranes of the neuroblastoma/glioma cell line NG 108-15. The importance of these structural differences and possible functional implications are discussed.