Archives of Toxicology

, Volume 65, Issue 1, pp 20–26 | Cite as

Cadmium/zinc-metallothionein induces DNA strand breaks in vitro

  • Thomas Müller
  • Rainer Schuckelt
  • Lothar Jaenicke
Original Investigations


The in vitro DNA strand breaking activity of metallothionein (MT) containing Cd2+ and Zn2+ in a molar ratio of 5∶2 is described. Studies with radical scavengers and electron paramagnetic resonance spectroscopy indicate that the DNA damage might be caused by a radical species formed by the native protein (i.e., MT) charged with the heavy metal ions. No DNA strand breaks are detectable with the heat-denatured MT or with Cd2+ or Zn2+ alone. Inhibition studies using EDTA as a metal ion chelator orN-ethylmaleimide to alkylate sulfhydryl groups suggest that both the bound heavy metal ions as well as the SH groups of the various cysteine residues of MT may be involved in the MT-dependent DNA cleavage. Further characterization showed that the DNA cleavage is more likely random than sequence- or base-specific. These observations may provide a clue in the search for initial events in Cd-related carcinogenicity.

Key words

Metallothionein DNA strand breaks Radicals 




rat MT2

metallothionein, isoform 2, isolated from rat liver

rabbit MT1

metallothionein, isoform 1, isolated from rabbit liver

rabbit MT2

metallothionein, isoform 2, isolated from rabbit liver




electron paramagnetic resonance


sodium dodecyl sulfate


covalently closed circular (supercoiled)


open circular




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Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • Thomas Müller
    • 1
  • Rainer Schuckelt
    • 2
  • Lothar Jaenicke
    • 2
  1. 1.INBIFO Institut für biologische ForschungKöln 90Federal Republic of Germany
  2. 2.Institut für BiochemieUniversität KölnKöln 1Federal Republic of Germany

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