Pulse Radiolysis Studies of the Interactions of the Sulfhydryl Compound Dithiothreitol and Sugars

Abstract

Pulse radiolysis studies of the hydrogen atom transfer ("repair") reaction from the sulfhydryl-containing (RSH) compound dithiothreitol (DTT) to the DNA sugar deoxyribose and to several related sugars have been undertaken. The H transfer reaction is measured by monitoring the transient absorbance of the radical-anion RSSR-. The H atom transfer reactions for some sugars were fitted by a single time exponential function, but other sugars exhibited both a fast and a slow component (approximately 10-fold difference in rates) to the reaction. The reaction rates for the slow stage of the reaction between DTT and the sugars ranged from 0.5 X 10(7) dm3 mole-1 sec-1 for ribose-5-phosphate to 9 X 10(7) dm3 mole-1 sec-1 for 2-deoxyglucose. The maximum extent of total repair varied from 60% for ribose-5-phosphate to 100% for 2-deoxyglucose. The rate of repair, the extent of repair, and the appearance of more than one component of repair seem to depend on several factors: The occurrence of radical-radical reactions in the system is indicated by the demonstration of a dose dependence of the reaction kinetics, and this affects the observed rate of formation of RSSR-. Sugars with a deoxy group on the 2-carbon atom seem to have enhanced rates and extents of repair and to exhibit both fast and slow components to the reaction. The presence of a phosphate group on the sugar causes a decrease in the rate and extent of repair. The biological relevance of the reactions studied herein is discussed and the rates obtained are compared with rates for repair of damage in certain radiobiological systems.