Neighboring Pyrrolidine Amide Participation in Thioether Oxidation. Methionine as a “Hopping” Site

Methionine residues have been shown to function as efficient “hopping” sites in long-range electron transfer in model polyprolyl peptides. We suggest that a key to this ability of methionine is stabilization of the transient sulfur radical cation by neighboring proline amide participation. That is, in a model system a neighboring pyrrolidine amide lowers the oxidation potential of the thioether by over 0.5 V by formation of a two-center three-electron SO bond.

研究表明，甲硫氨酸（Methionine）残基可作为模型聚脯氨酸肽中长程电子转移过程的高效“跳跃”位点。我们提出，甲硫氨酸具备该功能的核心机制，是其邻近的脯氨酸酰胺参与作用，对瞬态硫自由基阳离子实现稳定化。具体而言，在该模型体系中，邻近的吡咯烷酰胺可通过形成两中心三电子SO键，使硫醚的氧化电位降低超过0.5伏特。