Abstract
The influence of metallic ions such as Cd2+, Cu2+ and Hg2+ on the poly (A)·poly (U) duplex formed by an equimolar mixture of poly (A) and poly (U) was studied by using a modified differential scanning calorimeter (DSC) with a help of the spectral measurements.
The transition temperature, T1, of poly (A)·poly (U) duplex shows a definite value of about 315K which is nearly independent of r (the mole ratio of metallic ion to phosphate in polynucleotide).
While, the dependence of the heat of helix-coil transition, ΔH, on r was divided into two cases: in the first case, when r is less than 10-2, ΔH for Cu2+ and Cd2+ systems increases with an increase of r, but ΔH for Hg2+ system is a definite value which is nearly independent of r. In the second case, when r is in excess of 10-2, ΔH for all systems shows a drastic decrease as r increases.
From the results of spectral measurements obtained, poly (A)·poly (U) duplex seems to form a complex with Cu2+ or Hg2+ at room temperature when r is more than 10-2 except for Cd2+ system, and random coil structure of poly (A) and poly (U) obtained in which are the helix-coil transition of poly (A)·poly (U) duplex interacts also with metallic ions, and its interaction is expected to be exothermic. While, the behavior for Cd2+ system is the same to that of Cu2+ or Hg2+ system. However, the effects of poly (A)·poly (U) duplex on Cd2+ may differ from those of Cu2+ or Hg2+ systems.
