Superoxide-driven NAD(P)H oxidation induced by EDTA-manganese complex and mercaptoethanol.
A purely chemical system for NAD(P)H oxidation to biologically active NAD(P)+ has been developed and characterized. Suitable amounts of EDTA, manganous ions and mercaptoethanol, combined at physiological pH, induce nucleotide oxidation through a chain length also involving molecular oxygen, which eventually undergoes quantitative reduction to hydrogen peroxide. Mn2+ is specifically required for activity, while both EDTA and mercaptoethanol can be replaced by analogs. Optimal molar ratios of chelator/metal ion (2:1) yield an active coordination compound which catalyzes thiol autoxidation to thiyl radical. The latter is further oxidized to disulfide by molecular oxygen whose one-electron reduction generates superoxide radical. Superoxide dismutase (SOD) inhibits both thiol oxidation and oxygen consumption as well as oxidation of NAD(P)H if present in the mixture. A tentative scheme for the chain length occurring in the system is proposed according to stoichiometry of reactions involved. Two steps appear of special importance in nucleotide oxidation: (a) the supposed transient formation of NAD(P). from the reaction between NAD(P)H and thiyl radicals; (b) the oxidation of the reduced complex by superoxide to keep thiol oxidation cycling.
Paoletti
F
F
Istituto di Patologia Generale, Universita di Firenze, Italy.
Mocali
A
A
Aldinucci
D
D
D002384:Catalysis; D002614:Chelating Agents / Q000494:pharmacology; D004357:Drug Synergism; D004492:Edetic Acid / Q000494:pharmacology*; D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008345:Manganese / Q000494:pharmacology*; D008623:Mercaptoethanol / Q000494:pharmacology*; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*
D002614:Chelating Agents; D005609:Free Radicals; D013438:Sulfhydryl Compounds; D013481:Superoxides; D008345:Manganese; D009249:NADP; D008623:Mercaptoethanol; D004492:Edetic Acid; D006861:Hydrogen Peroxide