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.
Stanley
J S
JS
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205-7199.
York
J L
JL
Benson
A M
AM
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