Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.5.2 (NQO1)
 6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

NADH peroxidase is a flavoenzyme having a single redox-active thiol, Cys42, that cycles between sulfenate and thiol forms in the NADH-dependent reduction of hydrogen peroxide. NADH peroxidase catalyzes the NADH-dependent reduction of quinones with turnover numbers between 1.2 and 3.9 s-1, per mole of FAD, at pH 7.5. The bimolecular rate constants for quinone reduction, V/K, ranged from 4.3 x 10(3) to 6.0 x 10(5) M-1 s-1 for 14 quinones whose redox potentials varied between -0.41 and 0.09 V. The logarithms of the V/K values for these quinones are hyperbolically dependent on their single-electron reduction potentials (E7(1). One-electron reduction of benzoquinone accounts for about 50% of the total electron transfer catalyzed by NADH peroxidase at pH 7, with the remainder of the reduction being catalyzed by a two-electron (hydride) transfer. Cys42 can be irreversibly oxidized to the sulfonate by hydrogen peroxide, with inactivation of the peroxidatic activity of the enzyme. The residual quinone reductase activity of NADH peroxidase which has undergone oxidative inactivation of the active site Cys42 indicates that this residue is not involved in the reduction of the quinones. Product inhibition studies suggest the possibility of overlap of the pyridine nucleotide and quinone binding sites in the reduced enzyme at low pH values. The pH dependence of the maximum velocity of naphthoquinone reduction shows that deprotonation of an enzymic group, exhibiting a pK value of ca. 6.2, decreases the maximal velocity. Primary deuterium kinetic isotope effects on V and V/K for quinone-dependent NADH oxidation increase upon protonation of a group, exhibiting a pK value of 6.4.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Quinone reductase reaction catalyzed by Streptococcus faecalis NADH peroxidase. 775 94

Smith, S. L. (Cornell University, Ithaca, N.Y.), P. J. Van Demark, and J. Fabricant. Respiratory pathways in the Mycoplasma. I. Lactate oxidation by Mycoplasma gallisepticum. J. Bacteriol. 86:893-897. 1963.-Resting cells of Mycoplasma gallisepticum 293 required the addition of nicotinamide adenine dinucleotide, thiamine pyrophosphate, and flavine mononucleotide for the maximal rate of sodium lactate oxidation. Inhibitor studies, as well as spectrophotometric and chemical assays, indicate that the pathway of electron transport to oxygen during lactate oxidation does not involve heme catalysts, and is mediated by flavin-linked enzyme systems. The presence of reduced nicotinamide adenine dinucleotide-specific lactic dehydrogenase, menadione reductase, ferricyanide reductase, and reduced nicotinamide adenine dinucleotide oxidase activities was detected in cell-free extracts. No cytochrome c reductase or reduced nicotinamide adenine dinucleotide peroxidase activity was detected in these extracts.
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PMID:RESPIRATORY PATHWAYS IN THE MYCOPLASMA. I. LACTATE OXIDATION BY MYCOPLASMA GALLISEPTICUM. 1408 Jul 98