Abstract
The hypothesis was tested that Cd2+ undergoes measureable reaction with the Zn-proteome through metal ion exchange chemistry. The Zn-proteome of pig kidney LLC-PK1 cells is relatively inert to reaction with competing ligands, including Zinquin acid, EDTA, and apo-metallothionein. Upon reaction of Cd2+ with the Zn-proteome, Cd2+ associates with the proteome and near stoichiometric amounts of Zn2+ become reactive with these chelating agents. The results strongly support the hypothesis that Cd2+ displaces Zn2+ from native proteomic binding sites resulting in the formation of a Cd-proteome. Mobilized Zn2+ becomes adventitiously bound to proteome and available for reaction with added metal binding ligands. Cd-proteome and Zn-metallothionein readily exchange metal ions, raising the possibility that this reaction restores functionality to Cd-proteins. In a parallel experiment, cells were exposed to Cd2+ and pyrithione briefly to generate substantial proteome-bound Cd2+. Upon transition to a Cd2+ free medium, the cells generated new metallothionein protein over time that bound most of the proteomic Cd2+ as well as additional Zn2+.
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