title: Insights into the redox cycle of human quinone reductase 2.
abstract: NRH:quinone oxidoreductase 2 (QR2) is a cytosolic enzyme that catalyzes the reduction of quinones, such as menadione and co-enzymes Q. With the aim of understanding better the mechanisms of action of QR2, we approached this enzyme catalysis via electron paramagnetic resonance (EPR) measurements of the by-products of the QR2 redox cycle. The variation in the production of oxidative species such as H(2)O(2), and subsequent hydroxyl radical generation, was measured during the course of QR2 activity under aerobic conditions and using pure human enzyme. The effects on the activity of the following were compared: (i) synthetic (N-benzyldihydronicotinamide, BNAH) or natural (nicotinamide riboside, NRH) co-substrates; (ii) synthetic (menadione) or natural (co-enzyme Q0, Q2) substrates; (iii) QR2 modulators and inhibitors (melatonin, resveratrol and S29434); (iv) a pro-drug activated via a redox cycle [CB1954, 5-(aziridin-1-yl)-2,4-dinitrobenzamide]. The results were also compared with those obtained with human QR1. The production of hydroxyl radicals is: (i) observed whatever the substrate/co-substrate used; ii) quenched by adding catalase; (iii) not observed with the specific QR2 inhibitor S29434; (iv) observed with the pro-drug CB1954. While QR2 produced free radicals with this pro-drug, QR1 gave no EPR signal showing the strong reducing capacity of QR2. In conclusion, EPR analysis of QR2 enzyme activity through free radical production enables modulators and effective inhibitors to be distinguished.
authors.affiliation: Université de Toulouse 3, UPS, UMR 152 PHARMA-DEV, 118 route de Narbonne, F-31062 Toulouse cedex 9, France. reybier@cict.fr
authors.forename: Karine
authors.initials: K
authors.lastname: Reybier
authors.forename: Pierre
authors.initials: P
authors.lastname: Perio
authors.forename: Gilles
authors.initials: G
authors.lastname: Ferry
authors.forename: Jalloul
authors.initials: J
authors.lastname: Bouajila
authors.forename: Philippe
authors.initials: P
authors.lastname: Delagrange
authors.forename: Jean A
authors.initials: JA
authors.lastname: Boutin
authors.forename: Françoise
authors.initials: F
authors.lastname: Nepveu
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics; D001388:Aziridines / Q000493:pharmacokinetics; D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D051379:Mice; D010084:Oxidation-Reduction; D011355:Prodrugs / Q000493:pharmacokinetics; D011808:Quinone Reductases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000970:Antineoplastic Agents; D001388:Aziridines; D004791:Enzyme Inhibitors; D005609:Free Radicals; D011355:Prodrugs; C100099:tretazicar; D006861:Hydrogen Peroxide; C419642:NRH - quinone oxidoreductase2; D011808:Quinone Reductases