Time-resolved EPR studies on the reaction rates of peroxyl radicals of poly(acrylic acid) and of calf thymus DNA with glutathione. Re-examination of a rate constant for DNA

Abstract

Electron paramagnetic resonance (EPR) signals of peroxyl radicals of poly(acrylic acid), PAA, and of single- and double-stranded DNA were generated at 293 K and pH 6.6 by in situ photolysis of O2-saturated aqueous solutions containing the macromolecules and H2O2. From time-resolved EPR measurements upper limits for the rate constants of reaction of glutathione (GSH) with the peroxyl radicals of PAA [kb < or = (0.8 +/- 0.2) x 10(2) dm3 mol-1S-1] and of single- and double-stranded DNA from calf thymus [kb < or = (2 +/- 2) x 10(2) dm3 mol-1S-1] were determined. The low value of kb for reaction of GSH with DNA peroxyl radicals is in agreement with the observed lack of protective effect of the thiol in radiation-induced DNA strand break reactions (Liphard et al. 1990).