Oxygen toxicity. The influence of adenine-nucleotides and phosphate on Fe2+ autoxidation.

FeCl2 in Na phosphate buffer autoxidizes forming active oxygen species which damage deoxyribose. Di- and triphosphate adenine-nucleotides inhibit both Fe2+ autoxidation and deoxyribose damage in Na phosphate buffer pH 7.4. The inhibition is related to the number of charges of the adenine-nucleotide molecule: ATP at pH 7.4 is a better inhibitor than ADP; at a pH (6.5) close to the pK's of the third and fourth charge of ADP and ATP, ADP inhibition is greatly decreased whereas ATP inhibition is slightly affected. The extent of ATP inhibition of Fe2+ autoxidation depends both on ATP/Mg2+ and ATP/Fe2+ ratios in the reaction mixture. Formation of a Fe2+-nucleotide complex appears to be the mechanism through which ATP and ADP inhibit autoxidation and thus the generation of active oxygen species. These findings are discussed in relation to physiological and pathological fluctuations of nucleotide concentrations.