AN ELECTROSPRAY MASS-SPECTROMETRIC STUDY OF ORGANOMERCURY(II) AND MERCURIC INTERACTIONS WITH PEPTIDES INVOLVING CYSTEINYL LIGANDS

Positive ion electrospray mass spectrometry (MS) has been used to inve stigate the interaction of Hg2+, [MeHg](+) and [PhHg](+) cations with cysteine (Cys), glutathione (GSH) and a 27-residue polypeptide (Pp) co ntaining one cysteinyl sulfur located at the N-terminus. MS/MS experim ents showed that organomercury adduction occurs primarily at the sulfh ydryl group, with some evidence for isomeric species in which the orga nomercury cation is bound to either an amino or a carboxylic group, Fo llowing Ellman modification of GSH and Pp, the maximum number of adduc ted organomercury cations was reduced by 2 and 1, respectively, indica ting a 2:1 and a 1:1 interaction between [RHg](+) and the cysteinyl su lfur. Unlike [PhHg](+), [MeHg](+) showed an almost exclusive affinity for the cysteinyl sulfur of GSH and Pp. Both Cys and GSH reacted with Hg2+ to form polynuclear species. Collisional activation mass spectra of the [2Cys+Hg-H](+) ion indicated that the Hg (II) was most probably bridged between the two cysteinyl residues, although not necessarily via a conventional -S-Hg-S-linkage.