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

When a mixture of bovine brain G-proteins (Gi/o) was loaded onto an octyl sepharose column in the presence of AlF4-, alpha-subunits of molecular weights 39 kDa and the 41 kDa were eluted separately, followed by the appearance of two distinct peaks containing beta gamma-subunits (beta gamma-I, beta gamma-II). Both beta gamma-I and beta gamma-II possessed identical beta-subunits but different gamma-subunits. The molecular weights of the two gamma-subunits determined by SDS-polyacrylamide gel electrophoresis both in the presence and absence of urea were 4.5 kDa (gamma-I) and 5.0 kDa (gamma-II). Tests indicated that the two isolated gamma-subunits are intact and have not undergone proteolysis. The amino acid composition of gamma-I appeared to be distinct from that of gamma-II. Therefore, this method is a simple procedure for isolating beta gamma-I and beta gamma-II.