OXIDATION OF NICOTINAMIDE ADENINE-DINUCLEOTIDE BY HYDROPEROXYL RADICAL - FLASH-PHOTOLYSIS STUDY

The one-electron oxidation of nicotinamide adenine dinucleotide (NADH) by hydroperoxyl radical was studied over a broad range of reagent concentrations and pH values by the method of flash photolysis. Of the acid-base forms of the radical, HO2· and O2-·, only the first one is an active oxidant. The rate constant of the reaction HO2· + NADH → H2O2 + NAD· is equal to (1.8 ± 0.2) × 105 M-1 s-1 at 20°C. The temperature dependencies of the reaction rate at different pH values gave the activation energy of this reaction, Ea = 5.5 ± 0.5 kcal, as well as the standard enthalpy of the equilibrium HO2· ⇌ O2-· + H+, ΔH°= 2.7 ± 0.7 kcal. © 1979 American Chemical Society.