1.Role of the sulfur atom on the reactivity of methionine toward OH radicals: comparison with norleucine.
Francisco-Marquez M1, Galano A. J Phys Chem B. 2009 Apr 9;113(14):4947-52. doi: 10.1021/jp900118f.
Density functional theory has been used to model the OH reaction with Gly-Met-Gly and Gly-Nle-Gly tripeptides. The first one is predicted to be about 100 times faster than the second one. Therefore, if a methionine fragment is replaced by norleucine, the overall reactivity of the peptide toward free radicals is expected to be significantly reduced, which is in agreement with previous experimental findings. Since the most reactive sites were found to be located in the central backbone for Nle and in the terminal fragment of the side chain for Met, this decrease is expected to be even more critical for large-sized free radicals. The S atom seems to activate not only those alkyl sites next to it but also those located an odd number of bonds apart. In addition the viability of different paths explaining the formation of methionine sulfoxide has been tested, and it is proposed that this process involves the formation of R-SO radical and formaldehyde.
