Methionine-S-oxide reductase (, methyl sulfoxide reductase I and II, acetylmethionine sulfoxide reductase, methionine sulfoxide reductase, L-methionine:oxidized-thioredoxin S-oxidoreductase) is an enzyme with system name L-methionine:thioredoxin-disulfide S-oxidoreductase. This enzyme catalyses the following chemical reaction