Ferrous-salt-promoted damage to deoxyribose and benzoate. The increased effectiveness of hydroxyl-radical scavengers in the presence of EDTA

Hydroxyl radicals (OH.) in free solution react with scavengers at rates predictable from their known second-order rate constants. However, when OH. radicals are produced in biological systems by metal-ion-dependent Fenton-type reactions scavengers do not always appear to conform to these established rate constants. The detector molecules deoxyribose and benzoate were used to study damage by OH. involving a hydrogen-abstraction reaction and an aromatic hydroxylation. In the presence of EDTA the rate constant for the reaction of scavengers with OH. was generally higher than in the absence of EDTA. This radiomimetic effect of EDTA can be explained by the removal of iron from the detector molecule, where it brings about a site-specific reaction, by EDTA allowing more OH. radicals to escape into free solution to react with added scavengers. The deoxyribose assay, although chemically complex, in the presence of EDTA appears to give a simple and cheap method of obtaining rate constants for OH. reactions that compare well with those obtained by using pulse radiolysis.