[Changing characteristic viscosity of DNA interacting with Cu2+ and Mn2+ ions]

The interaction of DNA with Cu2+ and Mn2+ ions in low ionic strength solutions (10(-3) M NaCl) has been studied by the viscosimetry method. The DNA characteristic viscosity [eta] decreases sharply at low ion concentrations (addition of 10(-5) M Cu2+ leads to [eta] reduction by a factor of 1.4) and attains certain saturation at high concentrations, the saturation magnitude slightly depending on the ion type. The reduction is much lower in solutions containing bivalent ions, in concentration 2 X 10(-2) M NaCl. The experimental data for bivalent and monovalent (Na+) ions have been compared. The results are discussed in terms of equilibrium ion-DNA binding and compared with the Fixman theory. It is discussed if ion binding constants can be determined by visosimetry. It is shown that the cause of the viscosity reduction with time observed by some authors may be the action of DNAases activated by metal ions.