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

Abstract

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.