Enhanced oxidation of NAD(P)H by oxidants in the presence of dehydrogenases but no evidence for a superoxide-propagated chain oxidation of the bound coenzymes

Abstract

Recently we demonstrated that lactate dehydrogenase (LDH)-bound NADH is oxidized by O₂, H₂O₂, HNO₂ and peroxynitrite predominantly via a chain radical mechanism which is propagated by superoxide. Here we studied both whether other dehydrogenases also increase their coenzymes' reactivity towards these oxidants and whether a chain radical mechanism is operating. Almost all dehydrogenases increased the oxidation of their physiological coenzymes by at least one of the oxidants. The oxidation of NADH or NADPH depended both on the binding dehydrogenase and the applied oxidant and in some cases the reactions were remarkably fast. The highest rate constant (k = 370 M^{− 1} s^{− 1}) was found for the reaction of HNO₂ with NADH bound to alcohol dehydrogenase. Regardless of the applied oxidant, superoxide dismutase failed to inhibit the oxidation of protein-bound NADH and NADPH. We therefore conclude that several dehydrogenases increase the oxidation of NADH and/or NADPH by the employed set of oxidants in bimolecular reactions, but, unlike LDH, do not mediate a -dependent chain radical mechanism.

• Dehydrogenases
• pyridine nucleotides
• coenzymes
• enzyme binding
• oxidants
• superoxide

• LDH
• l-lactate dehydrogenase
• ADH
• alcohol dehydrogenase
• AlDH
• aldehyde dehydrogenase
• G6-PDH
• glucose-6-phosphate dehydrogenase
• GlDH
• glutamate dehydrogenase
• GAPDH
• glyceraldehyde-3-phosphate dehydrogenase
• ICDH
• isocitrate dehydrogenase
• MDH
• malate dehydrogenase
• SOD
• superoxide dismutase
• SIN-1
• 3-morpholino-sydnonimine
• DTPA
• diethylenetriamine-pentaacetic acid
• ONOO⁻
• oxoperoxonitrate(1 − )/peroxynitrite