The chaperone protein CopC from Pseudomonas syringae features high-affinity binding sites (K (D) ~ 10(-13) M) for both Cu(I) (Met-rich) and Cu(II) (His-rich). When presented with these sites in the apoprotein, electrospray ionisation mass spectrometry confirmed that cis-Pt(NH(3))(2)Cl(2) (cisplatin) and the fragments [Pt(II)L](2+) (L is 1,2-diaminoethane, 2,2'-bipyridine) occupied the Cu(I) site specifically in the 1:1 Pt-CopC adducts (purified by cation-exchange chromatography). The cis-Pt(NH(3))(2) fragment was not present in these adducts (the dominant product for cisplatin was Pt-CopC in which all original ligands were displaced), while bidentate ligands L were retained in LPt-CopC adducts. In the context of the Met-rich Cu(I) pump Ctr1 as a significant entry point for cisplatin into mammalian cells, the present work confirms the ability of Met-rich sites in proteins to remove all ligands from cisplatin. It focuses attention on the potential of proteins that are part of the natural copper transport pathways to sequester the drug. These pathways are worthy of further study at the molecular level.