An electrophoretic mobility shift assay for methionine sulfoxide in proteins.

Study of the posttranslational modification of methionine to its sulfoxide has been receiving increasing attention because of its implication in regulation of protein activity, but techniques for the detection of this modification remain limited. In particular, there has been no method to detect the oxidation of methionine on polyacrylamide gels. Here we demonstrate that alkylation of methionine introduces a charge change that shifts the mobility of the protein on an acidic gel relative to the alkylation-resistant sulfoxide form.