A concentration- and pH-dependent interaction of methylmercury with DNA was observed using UV absorption spectroscopy. Methylmercury interacts with the amino substituents of the base moeities of DNA at pH 7 0 where the methylmercury to DNA mole ratio was 8.62 resulting in destabilization or denaturation of DNA as evidenced by an increase in UV absorption at 260 nm. At pH 5.7 and 8. 0 and at methylmercury to DNA mole ratio of 8.62, hypochromicity was observed. Methylmercury interacts with the oxygen on the phosphate moeities to DNA at pH 5.7, 70, and 8.0 when the methylmercury to DNA mole ratio was 1.08 to 6.47 resulting in stabilization of DNA double helix as was evidenced by reduction of UV absorption at 260 nm. Addition of sodium chloride in the amount required to give methylmercury to sodium chloride mole ratio of 1 in denatured DNA recovers the original native DNA indicating preferential bonding of methylmercury with chloride over that with base moeities of DNA.
This work has been inspired by the idea that important and interesting information regarding the mechanism
of toxicity of methylmercury can be obtained by a study of its effect on DNA helicity.