DETERMINATION OF THE COMPLETE COVALENT STRUCTURE OF THE GAMMA(2) SUBUNIT OF BOVINE BRAIN G-PROTEINS BY MASS-SPECTROMETRY

The complete covalent structure of the gamma(2) subunit of bovine brai n G proteins was determined by peptide mapping using matrix-assisted l aser desorption ionization and electrospray ionization mass spectromet ry and by partial sequencing using tandem mass spectrometry. Fragments were identified in proteolytic digests corresponding to all predicted internal sequences of gamma(2), but not for N- or C-terminal sequence s. Fragments consistent with modifications of the terminal peptides we re observed, however. The presence of these postulated modifications w as verified by tandem mass spectrometry. These studies define the stru cture of the native protein and provide a basis for comparison to expr essed proteins. 1995 Academic Press, Inc.