ON THE ORIGIN OF THE ABUNDANCE DISTRIBUTION OF APOMYOGLOBIN MULTIPLY-CHARGED IONS IN ELECTROSPRAY MASS-SPECTROMETRY

The abundance distribution of multiply charged ions produced during th e electrospray process is thought to depend on the initial conformatio nal state of the analyte in solution and on solution chemistry, but wi th some proteins, including apomyoglobin, the correlation between solu tion and mass spectrometry data is unclear. In this study, we compare our results obtained by mass spectrometry with available data describi ng conformations and average number of charges of apomyoglobin in solu tion, A good correlation between average number of charges in solution and in the mass spectrum is only found for the pH 4.2 solution. We pr opose that the discrepancies between solution and electrospray ionizat ion mass spectrometry observed with apomyoglobin under other solution conditions can be mainly explained by (1) a preferential fragmentation of the highly charged ions in the source and (2) a variation of pH in the droplets during the electrospray process. (C) 1998 John Wiley & S ons, Ltd.