HIGH-RESOLUTION TANDEM MASS-SPECTROMETRY OF CARBONIC-ANHYDRASE

Electrospray ionization of carbonic anhydrase with ion dissociation yi elds amass spectrum from which the masses of > 100 isotopic clusters a re determined accurately, with the number of charges assigned directly from resolved isotopic peaks. Of these clusters, 80% correspond to fr agmentation at or near the amino acid proline. The masses of combinati ons of two, three, and four of these clusters sum to the molecular mas s with 0.1-Da accuracy, while further fragment ion dissociation provid es additional sequence information. The capability of this methodology to detect sequence variations is illustrated with an isozyme having a single amino acid replacement.