Radiosensitivity and Hydroxyl Radical Reactivity of Phosphate Esters as Measured by Radiation-induced Dephosphorylation

Summary

The yields of inorganic phosphate from irradiated phosphate esters of biological interest have been measured in the presence of various free-radical scavengers. These studies indicate that hydroxyl radical attack on the phosphate esters accounts for most of this damage. Competition kinetics using different hydroxyl radical scavengers whose reactivities are known have been used to estimate the rate-constants for the overall hydroxyl radical reactivities of the phosphate esters. The extent of hydroxyl-radical-induced dephosphorylation is very low for nucleotide derivatives, but high for some sugar and glycerol phosphates, reflecting the probability of hydroxyl radical abstraction at the α or β carbon atoms adjacent to the phosphate ester linkage. The hydroxyl radical reactivities of nucleotides, coenzymes, sugar phosphates and phospholipid components are all high (1-10 × 10⁹ M⁻¹ sec⁻¹), indicating the importance of hydroxyl radical attack in the inactivation of these components in living cells, although not necessarily by dephosphorylation.