FIG. 1.

Methionine oxidation and repair of methionine sulfoxide (MeSO) via the methionine sulfoxide reductases (MSRs), modified according to Hoshi and Heinemann (71). Oxidation of methionine results in MeSO formation. MeSOs may be repaired by MSRs. Reduction of MeSOs by MSRs leads to the oxidation of the catalytic cysteines in the active sites of the MSRs and to the formation of an intramolecular disulfide. MSRs are recycled due to the thioredoxin/thioredoxin reductase system (Trx/TrxR). Further oxidation of MeSOs leads to the generation of nonrepairable methionine sulfones.