Analysis of biological thiols: determination of thiol components of disulfides and thioesters.

This report describes a method for using selective cleavage of thioesters to allow differentiation between thioesters and disulfides. The method identifies thiol components (including glutathione, coenzyme A, and cysteine) of low-molecular-weight thioesters and disulfides in cell extracts, as well as thiols bound to protein via thioester or disulfide links. Thioesters were cleaved with 200 mM hydroxylamine under a nitrogen atmosphere in the presence of monobromobimane (mBBr), which forms a fluorescent derivative with the released thiol. For analysis of disulfides, thioesters were cleaved with hydroxylamine in the presence of N-ethylmaleimide to block released thiols: disulfides were then reduced with 10 mM dithiothreitol and subsequently labeled with mBBr. The bimane derivatives were identified and quantified using previously described HPLC methods (G. L. Newton, R. Dorian, and R. C. Fahey, 1981, Anal. Biochem. 114, 383-387). Traditional methods using dithiothreitol and sodium borohydride to cleave disulfides can also cleave thioesters and thus should not be used for specific analysis of disulfides.