Abstract
The chain oxidation of lactate dehydrogenase-bound NADH initiated by superoxide radicals and propagated by oxygen was studied with pulse radiolysis. The kinetic parameters were re-evaluated in a system with carefully purified reagents (water and other chemicals) and in the presence of EDTA. The rate constant for the oxidation of the enzyme-bound NADH by O2- is calculated from the observed pseudo-first order disappearance of NADH and the chain length (molecules of NADH oxidized per O2- anion generated in the pulse). It is (1.0 +/- 0.2) X 10(5) M-1 S-1, consistent within a 13-fold variation in lactate dehydrogenase. NADH complex concentration and with varying chain length up to 6.1. Based on experiments with varying pH values from 4.5 to 9.0, the rate constant for oxidation of enzyme-bound NADH by HO2 is estimated to be 2.0 X 10(6) M-1 S-1.
Highlights
NADH initiated by superoxide radicals and propagated by oxygen was studied with pulse radiolysis
The rate constant for the oxidation of the enzyme-bound NADH by O,m is calculated from the observed pseudo-first order disappearance of NADH and the chain length
HO, and O, react with lactate dehydrogenasel-bound at different rates, and that the nucleotide radical produced in either Reaction 3 or Reaction 4 reacts in turn with molecular oxygen (Reaction 5) to generate another superoxide radical
Summary
NADH initiated by superoxide radicals and propagated by oxygen was studied with pulse radiolysis. All radiation experiments were carried out at 23” in airsaturated 0.1 M formate solutions containing 0.1 mM EDTA, 0.05 M phosphate, and varying amounts of NADH and lactate dehydrogenase.
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