One- and two-electron reduction of quinones by rat liver subcellular fractions.
NAD(P)H-quinone (menadione, Trolox C quinone, and alpha-tocopherol quinone) reductase activity of rat liver subcellular fractions was observed optically at 340-400 nm, and oxygen radical generation was demonstrated using the ESR spin trap, 5,5'-dimethyl-1-pyrroline-1-oxide. NAD(P)H-menadione reductase activity of the fractions decreased in the order: cytosol > microsomes > plasma membranes. Although more than 65% of the activity of microsomes and plasma membranes was inhibited on the addition of dicoumarol, no change in the menadione-mediated formation of oxygen radicals by either fraction was observed. As judged from the intensity of ESR signals, the menadione-mediated oxygen radical formation by plasma membranes was only one-tenth as great as that by microsomes. No generation of oxygen radicals in the NAD(P)H-menadione reductase reaction by cytosol was found, and the activity was abolished in the presence of dicoumarol, an inhibitor of DT-diaphorase. It is concluded that plasma membranes reduce quinones by way of two-electron transfer and that the activity may prevent cellular quinone toxicity. NAD(P)H-alpha-tocopherol quinone reductase activity was confirmed in all cellular fractions [Hayashi et al. (1992) Biochem. Pharmacol. 44, 489-493] and this activity was also inhibited by dicoumarol, suggesting that it was due to DT-diaphorase.
Nakamura
M
M
Department of Biophysics, Hokkaido University, Sapporo.
Hayashi
T
T
D000818:Animals; D004583:Electrons; D005609:Free Radicals; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism*; D014810:Vitamin E / Q000031:analogs & derivatives / Q000378:metabolism; D014812:Vitamin K / Q000378:metabolism*
D005609:Free Radicals; D014812:Vitamin K; D014810:Vitamin E; C002421:tocopherylquinone; D016660:NAD(P)H Dehydrogenase (Quinone); D010100:Oxygen