Polarographic Behavior of Metal Phytochelatin Complexes

The polarographic characteristics of metal-phytochelatin complexes (Me-PC) extracted from the marine alga Phaeodactylum tricornutum were investigated by the use of differential pulse polarography (DPP) at dropping mercury electrode (DME). Four metal-phytochelatin complexes differing for the metal bound, namely Cd-, Pb-, Zn- and Cu-PC, were studied, and their polarographic behavior was compared with that of Cd,Zn-thionein and Zn-thionein of mammalian origin. The polarographic characteristics of Me-PC exhibit a dependence on the metal bound to the peptides and on the pH of the solution. Both the organic and inorganic part of Me-PC are electroactive and give polarographic responses depending on their chemical form in solution. Dissociation and formation processes were investigated. The order of stability of the complexes was K′Cu−PC > K′Pb−PC ≥ K′Cd−PC > K′Zn−PC. The same electrochemical mechanisms were found to characterize both the polarographic behavior of metallothioneins and metal-phytochelatin complexes.