 Typically, the thiolate of a redox reagent such as glutathione or dithiothreitol attacks the disulfide bond on a protein forming a "mixed disulfide bond" between the protein and the reagent.This mixed disulfide bond when attacked by another thiolate from the reagent, leaves the cysteine oxidized.In effect, the disulfide bond is transferred from the protein to the reagent in two steps, both thiol–disulfide exchange reactions.