The Influence of Mn on DNA structure in the presence of Na ions: A Raman spectroscopic study

The influence of Mn2+ 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 Mn2+ concentrations that varied between 0 and 600 mM. No condensation of DNA was observed at any of the Mn2+ concentrations. At 5 mM Mn2+ and 150 mM Na no significant influence of Mn2+ ions on the DNA structure can be observed. Compared with our previous results obtained at 10 mM Na ions, binding of Mn2+ 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 Mn2+ ions as judging from the Raman spectra. No evidence for DNA melting was identified. A high Mn2+ affinity for binding to guanine N7 and possibly, in a much lesser extent, to adenine have been found.