Reducing Offsite Modification using 2-mercaptoethanol for Proteome Analysis.

Alkylation of the thiol group in cysteine (Cys) residues using halide reagents is a significant step in proteomics. However, non-specific modifications to the N-terminus and other amino acids are known. Thus promiscuous offsite alkylation in the peptide further complicated the MS spectra and thus made the difficulty of identification and quantification of all peptides. 2-mercaptoethanol (2-ME) is not only a regent for the reduction of the disulfide bond but also is bound to the Cys residue. Furthermore, it is known that dimethyl sulfoxide (DMSO) enhances the disulfide bond formation. Thus, based on these facts, we developed a method for specifical modification of Cys residues using 2-ME and DMSO. The specific modification of Cys residue by 2-ME were promoted by the concentration-dependent manner of DMSO with quite less offsite modification reaction compared with recent procedures. This Cys-specific modification technique may not only improve the quantification of peptides containing cysteine but also enhance the quantification accuracy of all peptides.