Influence of Cu(II) on the interaction of sulfite with DNA.

The quantitative influence of Cu(II) on the interaction of eukaryotic DNA with sulfite (SO(3)(2-)), which is a derivative of sulfur dioxide in the human body, was studied using ultraviolet (UV) absorption spectrometry. The results showed that under physiological pH conditions, SO(3)(2-) reacted weakly with DNA at concentrations of up to 10(-1)M, at which point a rapid increase in the reaction constant and the reaction number of SO(3)(2-) with DNA was observed. The addition of Cu(II) at concentrations ranging from 6.67 x 10(-4) to 3.33 x 10(-3)M to DNA-SO(3)(2-) binary systems increased the reaction constant of SO(3)(2-) with DNA 41- to 115-fold at a low concentration of SO(3)(2-) (10(-3)M), and 4- to 84-fold at an intermediate concentration of SO(3)(2-) (10(-2)M), but had little influence on the reaction number of SO(3)(2-) with DNA compared with the absence of Cu(II). When the concentration of SO(3)(2-) reached 10(-1)M, the presence of Cu(II) reduced the reaction number but had no effect on the reaction constant of SO(3)(2-) with DNA. These results show that the efficiency of SO(3)(2-) is increased in the presence of Cu(II) at high concentrations of SO(3)(2-).