1996 Volume 21 Issue 3 Pages 209-217
This paper describes the induction of DT-diaphorase by xenobiotic treatment of riboflavin-deficient rats. Upon injection of β-naphthoflavone once a day for 3 successive days into male Wistar rats fed a riboflavin-supplemented diet for 4 weeks, the activity of DT-diaphorase in the cytosolic, mitochondrial, and microsomal fractions of rat liver increased several fold compared with that of the vehicle control. In the case of rats fed a riboflavin-deficient diet for 4 weeks, DT-diaphorase activity in the cytosolic fraction was markedly decreased and that in microsomes was somewhat diminished, whereas the activity in mitochondrial fraction did not change, compared with that of the above control. However, when the deficient rats were injected with β-naphthoflavone intraperitoneally, DT-diaphorase activity in the cytosolic, mitochondrial, and microsomal fractions increased in spite of a significant decrease in flavin levels in the body. These results indicate that DT-diaphorase is actually induced even under conditions of riboflavin deficiency and that the apoprotein of the enzyme takes up FAD to become holoenzyme, suggesting a redistribution of FAD among various flavoproteins in the liver of riboflavin-deficient rats upon administration of a xenobiotic. Among the activities of other flavoenzymes examined, the occurrence of the apoenzyme of glutathione reductase, thioredoxin reductase or NADPH-cytochrome P450 reductase was found upon the injection of β-naphthoflavone in the riboflavin-deficient rats, which might be an indication of the above-mentioned redistribution.
