OBSERVATION OF LARGE MULTIMERS IN THE ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY OF PEPTIDES

Large multimeric ions were detected from electrospray ionization (ESI) mass spectrometry of peptides, using a quadrupole mass spectrometer o f standard mass range. Multimers, up to heptamers, were seen for angio tensin I; and multimers, up to pentamers, were observed for renin subs trate. The appearance of the multimeric species could be controlled by manipulation of sampling conditions in the ESI interface. The relevan ce of the observation of large multimers to proposed mechanisms of ESI is discussed. Implications of the observation of large multimers to e fforts to deduce higher order structure of biomolecules from ESI mass spectrometric experiments are also noted.