IDENTIFICATION OF 3 FORMS OF THE GAMMA-SUBUNIT OF G-PROTEINS ISOLATED FROM BOVINE SPLEEN

We reported previously that G proteins from bovine spleen contain at least five forms of the γ subunit (designated S1 through S5), among which S1 and S5 have been identified as novel γ and γ2 subunits, respectively. In this study, we identified the other three forms of the γ subunit, namely, S2, S3 and S4. Amino acid sequences of proteolytic fragments obtained from S2, S3 and S4 coincided exactly with internal sequences of γ7, γ5 and γ2, respectively. However, sequence analysis of undigested S4 revealed that S4 was an N-terminally truncated form of γ2 while analysis of the C-terminal fragment by fast atom bombardment mass spectrometry revealed that the C-terminus of S4 seemed to be geranylgeranylated and carboxymethylated as is that of intact γ2. Thus, the three types of γ subunit obtained from bovine spleen were identified as γ7, γ5, and an N-terminally truncated γ2. © 1993 Academic Press, Inc.