Binding of copper and zinc to three cyanobacterial microcystins quantified by differential pulse polarography

Amanda V. Humble, Geoffrey M. Gadd, Geoffrey A. Codd (Lead / Corresponding author)

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    60 Citations (Scopus)


    Microcystins are a family of potently hepatotoxic heptapeptides which have been detected in a wide range of cyanobacteria. The novel application of polarography in the analysis of these cyclic peptides has demonstrated binding of copper and zinc to microcystins in the aqueous-phase at environmentally-relevant pH values. This electroanalytical technique measured the shift in reduction potential and decrease in height of metal polarogram peaks as a function of increasing microcystin concentration. The successive formation of intermediate complexes was investigated and the strength of coordination was evaluated in terms of a formation constant (K1) for each metal/microcystin combination. The effects of a single amino acid substitution on the formation constants of the heptapeptide was investigated with microcystin-LR, microcystin-LW and microcystin-LF. The calculated formation constants (log K1) indicated that all three microcystins are intermediate strength metal ligands and that substitution of arginine with either tryptophan (microcystin-LW) or phenylalanine (microcystin-LF) appeared to have no discernible effect on the overall binding capacity. Reducing the pH of the supporting electrolyte strongly influenced complexation of microcystin-LR with copper, indicating that at pH 5.5 only a weak labile complex was formed. Complexation between microcystin-LR and zinc, however, was not influenced as strongly by pH.

    Original languageEnglish
    Pages (from-to)1679-1686
    Number of pages8
    JournalWater Research
    Issue number7
    Publication statusPublished - Jul 1997


    • Blue-green algae
    • Copper
    • Cyanobacteria
    • Differential pulse polarography
    • Formation constants
    • Microcystins
    • Zinc

    ASJC Scopus subject areas

    • Ecological Modelling
    • Water Science and Technology
    • Waste Management and Disposal
    • Pollution


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