Binding sites of [Ru(bpy)2(H2O)2](BF4)2 with sulfur- and histidine-containing peptides studied by electrospray ionization mass spectrometry and tandem mass spectrometry.

The composition and binding sites of cis-[Ru(II)(bpy)2]2+-bound sulfur-containing peptides of Met-Arg-Phe-Ala, glutathione and oxidized glutathione, and also histidine-containing peptide of oxidized insulin B chain, were investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The composition of Ru(II)-containing peptides was precisely determined by ESI-MS, zoom scan and simulation of isotope distribution patterns. MS/MS analysis shows that, in sulfur-containing peptides, the Ru(II) complex prefers to anchor to a carboxyl group, although some other potential binding sites of thiol, thioether and N-terminal amino groups present in these peptides, and in oxidized insulin B chain, Ru(II) first anchors to His10, then either to the hydroxyl group of Thr27 or to the carboxyl group of Ala30. Its secondary structure and microenvironment surrounding the potential binding sites may affect the binding ability of cis-[Ru(II)(bpy)2]2+ to oxidized insulin B chain.