Peptide methionine sulfoxide reductase A, also known msrA, is an enzyme that catalyzes the reversible oxidation-reduction of methionine sulfoxide in proteins to methionine. This protein could have an important function as a repair enzyme for proteins that have been inactivated by oxidation. Recombinant E.coli msrA protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.