Two γ-subunits, γ-I and γ-II, complex with the same β-subunits in bovine brain G-proteins (Gi/o)

Abstract When a mixture of bovine brain G-proteins (Gi/o) was loaded onto an octyl sepharose column in the presence of AlF 4 − , α-subunits of molecular weights 39 kDa and the 41 kDa were eluted separately, followed by the appearance of two distinct peaks containing βγ-subunits (βγ-I, βγ-II). Both βγ-I and βγ-II possessed identical β-subunits but different γ-subunits. The molecular weights of the two γ-subunits determined by SDS-polyacrylamide gel electrophoresis both in the presence and absence of urea were 4.5 kDa (γ-I) and 5.0 kDa (γ-II). Tests indicated that the two isolated γ-subunits are intact and have not undergone proteolysis. The amino acid composition of γ-I appeared to be distinct from that of γ-II. Therefore, this method is a simple procedure for isolating βγ-I and βγ-II.