Identification of a Novel γ-Subunit from Bovine Brain GTP Binding Regulatory Proteins (Gi/o)

Abstract Heterogeneity of the γ-subunit of G proteins has been demonstrated by cDNA cloning and by partial sequence analyses. We have isolated two intact βγ-subunit isoforms from bovine brain Gi/o mixture, in which only γ subunits are distinct (Sohma, H.,et al. (1992) Biochem. Biophys. Res. Commun. 184, 175-182). In this study, we isolated the γ-subunit isoforms, γ-I and γ-II, and examined their amino acid sequences. Both γ-I and γ-II had blocked N-terminal amino acid residues, and the terminal amino acids of both were able to be truncated by an acylamino-acid-releasing enzyme. γ-I seemed to be identical with the γ-subunit reported elsewhere, while the γ-II appeared to be a novel protein. Antibodies to synthetic peptides based on the part of the amino acid sequences of γ-I and γ-II reacted specifically to γ-I and γ-II, respectively.