A BRAIN-SPECIFIC GAMMA-SUBUNIT OF G-PROTEIN FREED FROM THE CORRESPONDING BETA-SUBUNIT UNDER NONDENATURING CONDITIONS

It has generally been accepted that the beta and gamma subunits of G proteins are tightly associated and can only be dissociated under denaturing conditions. However, one form of the gamma subunit, free of the beta subunit, was isolated under non-denaturing conditions during the purification of beta gamma complexes from bovine brain. Amino acid sequence analysis revealed that the N-terminus of this gamma subunit was not blocked and its sequence was identical to that of a brain-specific gamma subunit, gamma(3). Among three forms of gamma subunits observed in bovine brain (gamma(2), gamma(3) and gamma(7)), was the only form that was not modified at the N-terminus. Although the physiological significance of the free form of gamma(3) is not clear, these results suggest that N-terminal modification of gamma subunits may be important for interaction with beta subunits.