Mass spectrometry assisted assignments of binding and cleavage sites of copper(II) and platinum(II) complexes towards oxidized insulin B chain

Interaction of cis-[Pt(en)(H2O)(2)](2+) and [CuL(H2O)](2+), where L is 2-[bis(2-aminoethyl)aminol ethanol, with oxidized insulin B chain in molar ratio of 1:1, 1:2 and 1:3 at pH 2.5 and 40 degrees C has been investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The results show that the binding sites of the two complexes with oxidized insulin B chain are terminal NH2, imidazole groups of His5 and His10. The hydrolytic cleavage studies show that the [CuL(H2O)](2+), upon a pendant hydroxyl group of the ligand, selectively cleaves the peptide bonds at Gly8-Ser9, Asn3-Gln4 and Phe1-Val2, and the cis-[Pt(en)(H2O)(2)](2+) Only cleaves the peptide bond at HislO-Leull. This is the first report of cis-[Pt(en)(H2O)(2)](2+)-promoted cleavage of His-X peptide bond. Copyright (c) 2006 John Wiley & Sons, Ltd.