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5150128 
Technical Report 
Liver microsomal DT diaphorase: noninvolvement in hydroxylation of benzo(a)pyrene 
West, SB; Huang, MT; Lu, AYH 
1977 
Yes 
Federation Proceedings
ISSN: 0014-9446 
36 
3 
959; 1977 
WOS:A1977CW31803639 
PESTAB. DT diaphorase, and enzyme found in the liver cytosol and microsomal membrane, catalyzes the oxidation of NADPH and NADP by various redox dyes and quinones, but its physiological function is still not known. It has been postulated based on the parallel induction of DT diaphorase activity and benzo(a)pyrene (BP) hydroxylase in rat liver by 3-methylcholanthrene (3MC) and 2,3,7,8-tetrachlorodibenzo-p-dioxin that DT diaphorase may function as an electron carrier in the microsomal hydroxylation of BP (Lind et al., B.B.R.C. 56: 392 (1974); Beatty et al., B.B.R.C. 68: 197 (1976)). We have concluded based on the following results that DT diaphorase is not involved in the hydroxylation of BP to its phenolic products. 1) A highly purified reconstituted system isolated from the microsomes of 3MC-treated rats consisting of cytochrome P-448, NADPH-cytochrome c reductase and synthetic dilauroyl phosphatidylcholine had no DT diaphorase activity, but hydroxylated BP at a faster rate than microsomes from 3MC-treated rats. 2) Dicumarol at concentrations known to inhibit DT disphorase activity did not affect the rate of BP hydroxylation in this reconstituted system. 3) Highly purified DT diaphorase isolated from the liver microsomes of 3MC-treated rats when added to this reconstituted system did not stimulate or inhibit BP hydroxylation, nor could it replace NADPH-cytochrome c reductase in supporting BP hydroxylation. (Author abstract by permission) (Abstract No. 3634)