[Evaluating the harmfulness of copper in aquatic environment by measuring the supercoiled structure change of plasmid...

The interaction of cupric ions with supercoiled DNA was investigated by agarose gel electrophoresis. Experimental results indicate that cupric ions could convert DNA structure from supercoiled to relaxed forms outside the cells in distilled water medium. At the levels of 10(-3) mol/L and 10(-4) mol/L copper, supercoiled DNA was totally converted into other forms of DNA after 24 hours. At a lower cupric level of 10(-6) mol/L, 52% supercoiled DNA was converted to other forms after 24 h and the relaxed form increased by 17% at 48h. Supercoiled form of DNA relaxed and gradually disappeared with the increase of incubation period of copper ions with the plasmid DNA. Supercoiled DNA degraded into other forms more rapidly at higher copper concentration. The percentages of different forms of DNA were related to copper concentration and incubation time. These results suggested that changes in supercoiled DNA structure may provide a rapid and sensitive method to assess the harmfulness of copper in aquatic environment.