Strong sequence homology exists between NADH peroxidase (NadPrx) and NADH oxidase (NadOxd) which can suggest that both genes originally diverged from a common ancestral sequence. NadPrx adn NadOxd share low level of identity with other members of the flavoprotein disulfide reductase classes. NadPrx as well as other pyridine nucleotide-disulphide reductases (PNDR) use the isoalloxazine ring of FAD to shuttle reducing equivalents from NAD(P)H to a Cys residue that is usually a part of a redox-active disulphide bridge. In a second step, the reduced disulphide reduces the substrate. Particular residues have been found to be highly conserved in within the FAD/NAD binding domain.
NADH peroxidase NADH + H+ +H2O2 → 2 H2O + NAD+
1) 2 NADH + 2 H+ +O2 → 2 H2O + 2 NAD+
2) NADH + H+ +H+ + O2 → H2O2 + NAD+
3) NADH + 2O2 → H+ + NAD+ + 2O2.
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