CONFORMATION OR CYTOCHROME-C STUDIED BY DEUTERIUM-EXCHANGE ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

Deuterium exchange of bovine cytochrome c has been monitored by electr ospray ionization mass spectrometry. Different charge-state distributi ons in the mass spectrum appear to represent different protein conform ations, but rapid interconversion of the conformations can lead to a c oincidence df the deuterium exchange rates. When interconversion is bl ocked, the conformation corresponding to higher m/z(lower charge) exch anges more slowly, indicating a tightly folded state. Furthermore, the data suggest that at least two conformations can have identical charg e-state distributions, but have different exchange rates. Thus, neithe r charge-state distribution nor deuterium exchange rate alone is a suf ficient indicator of protein conformation.