[Effect of bivalent copper ions on conformation of polyriboadenylic acid]

Ultraviolet differential spectra (UDS) and CD-spectra of poly (A) in the presence of Cu2+ ions are studied at different degrees of phosphate groups screening. The binding of cu2+ ions with bases of phosphates is shown to lead to disordering or to ordering respectively, of the mutual orientation of nucleotides. The UDS components due to conformation variations in poly (A) and association between Cu2+ ions and its bases are calculated. Comparison of the latter UDS-component with the differential spectrum of a protonated adenosine-monophosphate permits to assume that Cu2+ ions are in a coordination bond with N (1) adenine. The calculation of the concentration dependence of the binding constants indicates binding cooperativity and weak dependence on the screening degree of poly (A) phosphate groups.