Protein purification. Samples from all purification steps were confirmed by the SDS-PAGE analysis. The expressed Grx2 proteins were purified using the HisTrap column and then applied to the Superdex 75 gel chromatography column. The purified C15S mutant (A) and wild-type Grx2 (B) proteins show >98% purity. The migration of the molecular mass markers is indicated on the left.