THE TOXICITY OF AROMATIC NITROCOMPOUNDS TO BOVINE LEUKEMIA VIRUS-TRANSFORMED FIBROBLASTS - THE ROLE OF SINGLE-ELECTRON REDUCTION

Bovine leukemia virus-transformed lamb embryo fibroblasts (line FLK) p ossess activity of DT-diaphorase of ca. 260 U/mg protein and similar l evels of other NADP(H)-oxidizing enzymes: NADH:oxidase, 359 U/mg; NADP H:oxidase, 43 U/mg; NADH:cytochrome-e reductase, 141 U/mg; NADPH:cytoc hrome-e reductase, 43 U/mg. In general, the toxicity of aromatic nitro compounds towards FLK cells increases on increase of single-electron r eduction potentials (E(7)(1)) of nitrocompounds or the log of their re duction rate constants by single-electron-transferring enzymes, micros omal NADPH:cytochrome P-450 reductase (EC 1.6.2.4) and mitochondrial N ADH:ubiquinone reductase (EC 1.6.99.3). No correlation between the tox icity and reduction rate of nitrocompounds by rat liver DT-diaphorase (EC 1.6.99.2) was observed. The toxicity is not significantly affected by dicumarol, an inhibitor of DT-diaphorase. Nitrocompounds examined were poor substrates for DT-diaphorase, being 10(4) times less active than menadione. Their poor reactivity is most probably determined by t heir preferential binding to a NADPH binding site, but not to menadion e binding site of diaphorase. These data indicate that at comparable a ctivities of DT-diaphorase and single-electron-transferring NAD(P)H de hydrogenases in the cell, the toxicity of nitrocompounds will be deter mined mainly by their single-electron reduction reactions.