The interactions between nucleic acids and polyamines. I. High resolution carbon-13 and hydrogen-1 nuclear magnetic resonance studies of spermidine and 5'-AMP.

In 0.5 M solution at pH 7.6, interaction of spermidine and 5'-AMP is demonstrated by downfield proton NMR shifts. Shifts of ribose and adenine protons support a model in which triprotonated spermidine engages the phosphate anion with the C-3 diamine segment in a conformation to maximize interaction and the C-4 amino segment extended to interact with adenine N-7 (base anti, 2' endo, g'g' and gg nucleoside conformation). Changes in carbon-13 chemical shifts fro ribose C-5' (downfield), C-2' C-3', and C-4' (upfield) and for adenine C-6 and C-8 (upfield) support this model. In 0.006 M solution no significant changes in proton shifts and therefore no evidence for interaction was found. Spermidine and 5' -UMP (0.006 M) showed interaction at pH 10.5 (small upfield shifts in the proton nmr) interpreted as changing conformation by solvent interaction. In 0.00l M 3'-UMP at pH 10.5 small downfield proton shifts induced by spermidine are attributed to interactions with phosphate anion.