Fig. 1

Spontaneous chemical conversion of cysteine by reacting with atmospheric oxygen to produce cystine and effect to avoid the conversion by the treatment of chemical derivatization of thiol group of cysteine utilizing monobromobimane. a Reaction of thiol molecule and monobromobimane. b Schematic representation of the experimental procedures. Briefly, cysteine aqueous solution prepared at the time of use was immediately treated by adding mBBr solution (denoted as “+ mBBr”) or only its solvent (denoted as “No mBBr”). The solutions were incubated under atmospheric conditions and then intermittently subjected to the measurement by LC–MS/MS analysis (see “Materials and methods”). c Time course of cysteine-bimane content in “mBBr treatment” solution (closed circle) and cysteine content in “No mBBr treatment” solution (open diamond). d Time course of cystine content in “mBBr treatment” solution (closed circle) and “No mBBr treatment” solution (open diamond). The contents were determined as the peak area in mass chromatogram monitoring m/z characteristic of individual target compounds, and are represented as the normalized peak area after normalization with that of internal standard. Data values are mean ± SE (n = 3)