title: Cysteine oxidation by the superoxide radical: a theoretical study.
abstract: The cysteine residue oxidation by the superoxide radical in the gas phase and in aqueous solution is studied using the integrated molecular orbital+molecular orbital (IMOMO) method combining the quadratic configuration interaction [QCISD(T)] and density functional (DFT) methods. The molecular environment effects are systematically investigated by considering two alternative directions of attack of the superoxide radical on the thiol and two different cysteine residue conformations. It is found that hydrogen bonding and the electrostatic interactions between the superoxide radical and cysteine side chain significantly affect the reaction energy barrier, as compared to that derived for the simple thiol model methanethiol. Among the two possible reaction channels, the one involving the sulfinyl radical formation is predicted to be the dominant channel in aqueous solution. In a highly hydrophobic environment the thiyl radical formation channel becomes the main cysteine oxidation channel.
authors.affiliation: Laboratoire de Chimie Physique et Rayonnements UMR CEA, University of Franche-Comte, E4, 16 route de Gray, 25030 Besançon Cedex, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Cardey
authors.forename: Mironel
authors.initials: M
authors.lastname: Enescu