The influence of Mn2+ on DNA structure in the presence of Na+ ions: a Raman spectroscopic study

The influence of Mn(2+) ions on the structure of natural calf thymus DNA was studied by Raman spectroscopy. Measurements were done at room temperature and pH 6.2±0.2, in the presence of the physiological concentration of 150 mM Na+ ions, and in the presence of Mn(2+) concentrations that varied between 0 and 600 mM. No condensation of DNA was observed at any of the Mn(2+) concentrations. At 5 mM Mn(2+) and 150 mM Na(+) no significant influence of Mn(2+) ions on the DNA structure can be observed. Compared with our previous results obtained at 10 mM Na(+) ions, binding of Mn(2+) ions to charged phosphate groups and to DNA bases is inhibited in the presence of 150 mM Na(+) ions. DNA backbone conformational changes were not observed in the whole concentration range of Mn(2+) ions as judging from the Raman spectra. No evidence for DNA melting was identified. A high Mn(2+) affinity for binding to guanine N7 and possibly, in a much lesser extent, to adenine have been found