Nitroreductases and glutathione transferases that act on 4-nitroquinoline 1-oxide and their differential induction by butylated hydroxyanisole in mice.
These studies concern the initial steps in 4-nitroquinoline 1-oxide (4NQO) metabolism in relation to mechanisms of anticarcinogenesis. Butylated hydroxyanisole (BHA) administration by a protocol known to inhibit the pulmonary tumorigenicity of 4NQO in A/HeJ mice enhanced hepatic and pulmonary activities for 4NQO metabolism by two major pathways, conjugative detoxification and nitroreductive activation. High-performance liquid chromatography analysis showed approximate doubling of two types of glutathione transferase subunits with 4NQO-conjugating activity in livers of BHA-treated mice. Similar increases were observed in hepatic 4NQO-conjugating activity and in Vmax, while Km for 4NQO was 39 to 43 microM. Pulmonary 4NQO-glutathione transferase activity increased 24 to 29%. DT diaphorase activity toward 4NQO was elevated 3.3-fold in livers and 2.7-fold in lungs of BHA-treated mice. However, the predominant 4NQO reductase of liver and lung was dicumarol resistant, had a strong preference for NADH, and showed little if any response to BHA. This Mr 200,000 enzyme, partially purified from livers of Swiss mice, exhibited the stoichiometry of 2-NADH/4NQO expected for reduction of 4NQO to 4-hydroxyaminoquinoline 1-oxide. Its high affinity for 4NQO (Km, 15 microM) signified a much greater influence on 4NQO metabolism than DT diaphorase (Km, 208 microM). The dicumarol-resistant 4NQO reductase differed from several known cytosolic nitroreductases. The results suggest that protection by BHA may result from alteration of the balance between 4NQO activation and conjugation.
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205-7199.
J S
JS
Stanley
J L
JL
York
A M
AM
Benson
D015112:4-Nitroquinoline-1-oxide / Q000378:metabolism*; D000818:Animals; D002083:Butylated Hydroxyanisole / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000378:metabolism; D001728:Dicumarol / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D004947:Esophagus / Q000201:enzymology; D005260:Female; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000032:analysis / Q000096:biosynthesis*; D008099:Liver / Q000201:enzymology; D008168:Lung / Q000201:enzymology; D051379:Mice; D009243:NAD / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000096:biosynthesis; D009601:Nitroreductases / Q000032:analysis / Q000096:biosynthesis*; D014969:Xanthine Oxidase / Q000096:biosynthesis
D009243:NAD; D002083:Butylated Hydroxyanisole; D015112:4-Nitroquinoline-1-oxide; D001728:Dicumarol; D014969:Xanthine Oxidase; D016660:NAD(P)H Dehydrogenase (Quinone); D009601:Nitroreductases; D005982:Glutathione Transferase; D005978:Glutathione