HIGH-ENERGY COLLISION-INDUCED DISSOCIATION OF MULTIPLY-CHARGED POLYPEPTIDES PRODUCED BY ELECTROSPRAY

The recent commercial implementation of an electrospray source on a fo ur-sector mass spectrometer has allowed the study of high-energy colli sional activation of multiply charged cations. With this configuration , higher mass-to-charge ratios can be accommodated in both precursor i on selection and fragment ion detection. Good mass accuracy facilitate s analysis of fragment ions and allows more reliable mechanistic corre lation of these fragments. A convenient scheme was devised to permit t he use of kilovolt potentials in both MS-1 and MS-II, with precursors of varying charge states. Algorithms were devised to assign masses of different types of multiply charged fragment ions. Nine polypeptides w ere studied in the mass range 2000-5000 Da. Through this entire mass r ange, fragment ions were observed to be amply formed by cleavages in b oth the backbone and side chains, analogous to high-energy collisional activation of singly charged ions. This stands in sharp contrast to t he patterns reported with low-energy, multiple collisions. Abundances of sequence ion series are influenced by the positions of basic residu es. Analysis of charge distributions in fragment ions also indicates t hat the charges tend to be spread out across the peptides.