Shinji Nonose

Temperature Dependence of Gas-Phase Conformations for Protein and Peptide Ions Characterized by Proton Transfer Reactions with Gaseous Molecules

Keywords: Proton transfer, Multiply-protonated protein and peptide ion, Absolute reaction rate constant, Temperature dependence, Conformation change

Proton transfer from multiply-protonated protein ions to gaseous molecules was studied in the gas phase. Absolute reaction rate constants for proton transfer were determined from intensities of parent and product ions in the mass spectra. Temperature dependence of reaction rate constants and branching fractions for proton transfer was measured. An issue that is attracting considerable attention is vacuo conformations might resemble structural evolution that originated from temperature in the gas phase.

A home-made tandem mass spectrometer with electrospray ionization (ESI) was used for measurements. Multiply-charged protein ions were produced by ESI of a dilute solution of proteins in methanol-water mixture including acetic acid. We chose disulfide-intact lysozyme, disulfide-reduced lysozyme, cytochrome c, myoglobin, ubiquitin, as sample proteins. The ions produced by ESI were admitted into the vacuum chamber through stainless capillary. The charge-selected protein ions emerging from a quadrupole mass spectrometer (QMASS) were admitted into a collision cell with octapole ion trap. The collision cell was filled with He including gaseous molecules. We chose 1-propylamine, 1-butylamine, 1-pentylamine, tert-butylamine, diethylamine, dipropylamine, pyridine, 2-methylpyridine, or 2,6-dimethylpyridine as target molecules. Temperature dependence of reaction rates and branching fractions for proton transfer from multiply-charged protein ions to the target molecules was measured, by changing temperature of the collision cell. The parent and product ions were mass-analyzed by a time-of-flight mass spectrometer equipped with reflectron.