Targeted binding of a platinum(II)–methionine complex to the disulfide linkage of a nonapeptide oxytocin

The electrospray mass spectrometry and NMR spectroscopy techniques reveal that the platinum(II)–methionine complex [Pt(Met)Cl2] binds to the disulfide bond between Cys1 and Cys6 residues of oxytocin (OT). The major adducts identified are [Pt(Met)(OT)]Cl2 species where OT forms five- or six-membered chelates with Pt(II) center. The study suggests that even the oxidized disulfide in oligopeptide still shows a high affinity for platinum complexes, which may be associated with the ubiquity of sulfur-related side effects in platinum anticancer chemotherapy.