Hi.We are trying to prepare heavy atom derivatives of a protein in which a surface residue was mutated to cysteine. Mass spectrometry of the purified cysteine mutant showed an additional peak with a molecular mass that correspond to a mercaptoethanol-bound cysteine mutant. I am wondering whether the bound mercaptoethanol prevents the heavy atom from binding to the cysteine residue.
Any information would be greatly appreciated. Wataru Kagawa
