The identification of biologically important thiols.

A new mass spectral method has been developed and used to identify biologically important thiols. This method is based upon the use of C-14 labeled N-para-bromophenylmaleimide (BPM) to selectively derivatize thiols. The isotopic label facilitates the isolation and purification of trace quantities of the maleimide thiol adducts by high performance liquid chromatography (HPLC) with radioactivity detection. The use of the bromine atom in the thiol derivative greatly enhances the detectability of the parent and fragment ions containing the BPM moiety because of the generation of the characteristic N + 2 doublet ions. Several examples of the use of this method to identify non-volatile thiol peptides such as glutathione (GSH) and homoglutathione (hGSH) by fast atom bombardment mass spectrometry (FAB-MS) are described in this report.