Structure and Reactivity of the Glutathione Radical Cation: Radical Rearrangement from the Cysteine Sulfur to the Glutamic Acid alpha-Carbon Atom

A gas-phase radical rearrangement through intramolecular hydrogen-atom transfer (HAT) was studied in the glutathione radical cation, [-ECG](+.), which was generated by a homolytic cleavage of the protonated S-nitrosoglutathione. Ion-molecule reactions suggested that the radical migrates from the original sulfur position to one of the -carbon atoms. Experiments on the radical cations of dipeptides derived from the glutathione sequence, [-EC](+.) and [CG](+.), pointed to the glutamic acid -carbon atom as the most likely site of the radical migration. Infrared multiple-photon dissociation (IRMPD) spectroscopy was employed to generate complementary information. IRMPD of [-ECG](+.) in the approximately 1000-1800cm(-1) region was inconclusive owing to the relatively broad, overlapping absorption bands. However, the IRMPD spectrum of [-EC](+.) in this region was consistent with the radical migrating from the sulfur to the -carbon atom of glutamic acid. IRMPD in the 2800-3700cm(-1) region performed on [-ECG](+.) is consistent with a mixture of both the original sulfur-based radical and the resulting glutamic acid -carbon-based species. Comparisons are made with previously published condensed and gas-phase studies on intramolecular HAT in glutathione.