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Positive ion electrospray mass spectrometry (MS) has been used to investigate the interaction of Hg 1 +, [MeHg]+ and [Phflg]" cations with cysteine (Cys), glutathione (GSH) and a 27-residue polypeptide (Pp) containing one cysteinyl sulfur located at the N-terminus. MSIMS experiments showed that organomercury adduction occurs primarily at the sulfhydryl group, with some evidence for isomeric species in which the organomercury cation is bound to either an amino or a carboxylic group. Following Ellman modification of GSH and Pp, the maximum number of adducted organomercury cations was reduced by 2 and 1, respectively, indicating a 2 : 1 and a 1 : 1 interaction between [RHgr and the cysteinyl sulfur. Unlike [Phflg]", [MeHgr showed an almost exclusive affinity for the cysteinyl sulfur of GSH and Pp, Both Cys and GSH reacted with Hg 1+ to form polynuclear species. Collisional activation mass spectra of the [2Cys + Hg -H]" ion indicated that the Hg(I1) was most probably bridged between the two cysteinyl residues, although not necessarily via a conventional-S-Hg-S-linkage.

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