Lifetime of Peroxyl Radicals of Poly(U), Poly(A) and Single-and Double-Stranded DNA and the Rate of Their Reaction with Thiols

Summary

Peroxyl radicals of poly(U), poly(A), and single- and double-stranded DNA have been produced by photolysing H₂O₂ in oxygenated aqueous solution in presence of the substrates. The peroxyl radicals are formed by the reaction of OH radicals with the polynucleotides followed by addition of oxygen.

The lifetime of the peroxyl radicals and the rate constant of their reactions with the thiols cysteamine, gluthathione and dithiothreithol have been measured by time-resolved e.s.r. spectroscopy. The unusually long lifetimes range from 0·2 to 3·3 s. The activation energy for the decay for all four substrates is 10·3 ± 1 kcal/mol (43 kJ mol⁻¹). The reaction rate constants with the thiols range from k = 0·8 × 10⁴ to 1·3 × 10⁵ dm³ mol⁻¹ s⁻¹. The reactions of the thiols with the peroxyl radical of poly(U) are known to prevent strand break formation. This shows that the peroxyl radicals of poly(U) observed by e.s.r. are intermediates in the pathway leading to strand break formation.

• peroxyl radicals of DNA
• polyuridylic acid
• polynucleotides
• time-resolved e.s.r.