-!- The reaction occurs in the reverse direction to that shown above. -!- Exhibits high specificity for reduction of the R-form of methionine S-oxide, with higher activity being observed with L-methionine S-oxide than with D-methionine S-oxide. -!- While both free and protein-bound methionine (R)-S-oxide act as substrates, the activity with the peptide-bound form is far greater. -!- Plays a role in preventing oxidative-stress damage caused by reactive oxygen species by reducing the oxidized form of methionine back to methionine and thereby reactivating peptides that had been damaged. -!- The reaction proceeds via a sulfenic-acid intermediate. -!- For MsrB2 and MsrB3, thioredoxin is a poor reducing agent but thionein works well.

-!- The reaction occurs in the reverse direction to that shown above. -!- Exhibits high specificity for the reduction of the S-form of L-methionine S-oxide, acting faster on the residue in a peptide than on the free amino acid. -!- On the free amino acid, it can also reduce D-methionine (S)-S-oxide but more slowly. -!- Plays a role in preventing oxidative-stress damage caused by reactive oxygen species by reducing the oxidized form of methionine back to methionine and thereby reactivating peptides that had been damaged. -!- The reaction proceeds via a sulfenic-acid intermediate. -!- Formerly EC 1.8.4.6.