野々瀬 真司

自作の二重質量分析装置を用いて、独自の研究をすすめています

当研究室では、真空中で孤立状態にあるタンパク質・ペプチド等の生体分子イオンと気体分子との間の、プロトン移動反応について研究しています。反応速度の温度変化から、生体分子イオンの立体構造の転移が分かりました。その結果、生命現象の反応素過程にも関連する、生体分子の協同的・組織的な相互作用について解明しました。実験には、自作のESI・二重質量分析・衝突反応装置を用いています。装置の自作には、広範な知識や熟練した技術と長い年月が要求されます。しかし、独自の研究を推進するには自作の装置が是非必要なのです。目的に向かって粘り強く努力し続けることは、研究だけではなく人生全般でも重要です。

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.