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)(H 2 O) 2 ] 2+ and [CuL(H 2 O)] 2+ , where L is 2‐[bis(2‐aminoethyl)amino]ethanol, with oxidized insulin B chain in molar ratio of 1 : 1, 1 : 2 and 1 : 3 at pH 2.5 and 40 °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 NH 2 , imidazole groups of His5 and His10. The hydrolytic cleavage studies show that the [CuL(H 2 O)] 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)(H 2 O) 2 ] 2+ only cleaves the peptide bond at His10–Leu11. This is the first report of cis ‐[Pt(en)(H 2 O) 2 ] 2+ ‐promoted cleavage of His–X peptide bond. Copyright © 2006 John Wiley & Sons, Ltd.