GAS-PHASE FOLDING AND UNFOLDING OF CYTOCHROME-C CATIONS

Water is thought to play a dominant role in protein folding, yet gaseo us multiply protonated proteins from which the water has been complete ly removed show hydrogen/deuterium (H/D) exchange behavior similar to that used to identify conformations in solution. Indicative of the gas -phase accessibility to D2O, multiply-charged (6+ to 17+) cytochrome c cations exchange at six (or more) distinct levels of 64 to 173 out of 198 exchangeable H atoms, with the 132 H level found at charge values 8+ to 17+. Infrared laser heating and fast collisions can apparently induce ions to unfold to exchange at a higher distinct level, while ch argestripping ions to lower charge values yields apparent folding as w ell as unfolding.