Prevention by Ce3+ of DNA destruction caused by Hg2+ in fish intestine

The interactions between Hg2+, Ce3+, and the mixture of Ce3+ and Hg2+, and DNA from fish intestine in vitro were investigated by using absorption spectrum and fluorescence emission spectrum. The ultraviolet absorption spectra indicated that the addition of Hg2+, Ce3+, and the mixture of Ce3+ and Hg2+ to DNA generated an obviously hypochromic effect. Meanwhile, the peak of DNA at 205.2 nm blue-shifted and at 258.2 nm red-shifted. The size of the hypochromic effect and the peak shift of DNA by metal ion treatments was Hg2+>Hg2++Ce3+>Ce3+. The fluorescence emission spectra showed that with the addition of Hg2+, Ce3+, and the mixture of Ce3+ and Hg2+ the emission peak at about 416.2 nm of DNA did not obviously change, but the intensity reduced gradually and the sequence was Hg2+>Hg2++ Ce3+>Ce3+. Hg2+, Ce3+, and the mixture of Ce3+ and Hg2+ had 1.12, 0.19, and 0.41 binding sites to DNA, respectively; the fluorescence quenching of DNA caused by the metal ions all attributed to static quenching. The binding constants (KA) of binding sites were 8.98 x 104 L/mol and 1.02 x 104 L/mol, 5.12 x 104 L/mol and 1.10 x 103 L/mol, 6.66 x 104 L/mol and 2.36 x 103 L/mol, respectively. The results showed that Ce3+ could relieve the destruction of Hg2+ on the DNA structure.