Kinetic study by pulse radiolysis of the lactate dehydrogenase-catalyzed chain oxidation of nicotinamide adenine dinucleotide by HO2 and O2- radicals

The lactate dehydrogenase-catalyzed chain oxidation of NADH (LDH-NADH) by the superoxide radicals, HO2 and O2, has been studied with pulse radiolysis in the pH range between 4.5 and 9.0. The rate constants for the oxidation of the LDH-NADH by HO2 and O2 determined at 23 degrees are 1.2 times 10-6 M(-1) s(-1) and 3.6 times 10-4 M(-1) s(-1), respectively. The latter represents an activation of over 1000-fold by the enzyme. A chain reaction mechanism consistent with the results from these kinetic studies has been proposed.