The influence of polyamine-nucleic acid complexes on Fe2+ autoxidation

Polyamines are able to affect Fe2+ autoxidation in the presence of suitable low molecular weight phosphorus-containing compounds; the inhibitory effect exerted by polyamines is directly related to their ability to bind phosphorus-containing compounds. It is well known that polyamines, as polycations at physiological pH, bind strongly to nucleic acids. In this paper it is shown that polyamines, also in the presence of nucleic acids, inhibit Fe2+ autoxidation and thus depress the generation of free oxygen radicals. Most of the nucleic acids tested inhibited Fe2+ autoxidation although the concentration which causes half maximal effect differs. Polyamine effect on Fe2+ autoxidation varies greatly depending on the single or double stranded nature of the nucleic acid. In the present of single stranded nucleic acids, spermine and spermidine potentiate the inhibition of Fe2+ autoxidation by these nucleic acids. A relationship exists between the ability of spermine to interact with single stranded nucleic acids and to inhibit Fe2+ autoxidation in their presence. When double stranded nucleic acids are present, polyamines reverse the inhibition of Fe2+ autoxidation exerted by these nucleic acids. Molecular mechanisms are proposed to explain these experimental results. The hypothesis that polyamines may inhibit oxidative damage caused to nucleic acids by Fe2+ autoxidation, is also discussed.