Temperature dependence of gas-phase conformations for ubiquitin ions characterized by proton transfer reactions

Temperature-Resolved Proton Transfer Reactions of Biomolecular Ions

Temperature-resolved proton transfer reactions of multiply-protonated angiotensin I, disulfide-intact and -reduced lysozyme, and ubiquitin ions to primary, secondary and aromatic amines were examined in the gas phase. Absolute reaction rate constants for the proton transfer were determined from the intensities of the parent and product ions in mass spectra. Dramatic changes were observed in the distribution of product ions and the reaction rate constants. In particular, the rate constants for disulfide-intact lysozyme ions changed more drastically with the change in charge state and temperature compared to the corresponding values for disulfide-reduced ions. Proton transfer reactions were enhanced or suppressed as the result of the formation of complexes between the ions with gaseous molecules, which is related to changes in their conformation with changing.

Conformations of disulfide-intact and -reduced lysozyme ions probed by proton-transfer reactions at various temperatures

Proton-transfer reactions of disulfide-intact and -reduced lysozyme ions (7+ through 14+) to 2,6-dimethylpyridine were examined in the gas phase using tandem mass spectrometry with electrospray ionization. By changing temperature of a collision cell from 280 to 460 K, temperature dependence of reaction rate constants and branching fractions was measured. Absolute reaction rate constants for the protein ions of specific charge states were determined from intensities of parent and product ions in the mass spectra. Remarkable change was observed for the rate constants and distribution of product ions. The rate constants for disulfide-intact ions changed more drastically with change of charge states and temperature than those for disulfide-reduced ions. Observed branching fractions for parent and product ions were represented by calculated reaction rate constants with a scheme of sequential process. The reaction rate constants are closely related to conformation changes with change of temperature, which are profoundly influenced by amputation of disulfide bonds.