title: Enzymic cis-trans isomerization of nitrofuran derivatives: isomerizing activity of xanthine oxidase, lipoyl dehydrogenase, DT-diaphorase and liver microsomes.
abstract: Xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) supplemented with an electron donor could catalyze the cis-trans isomerization of 3-(5-nitro-2-furyl)-2-(2-furyl)acrylamide, 3-(5-nitro-2-furyl)-2-phenylacrylamide and 3-(5-nitro-2-furyl)-2-(2-furyl)acrylonitrile. The direction of isomerization (cis leads to trans, cis in equilibrium trans or trans leads to cis) is dependent on the chemical structure of these nitrofuran derivatives. Lipoyl dehydrogenase (NADH:lipoamide oxidereductase, EC 1.6.4.3), DT-diaphorase (NAD(P)H:(quinone-acceptor) oxidoreductase, EC 1.6.99.2) and liver microsomes could also catalyze the conversion of cis-3-(5-nitro-2-furyl)-2-(2-furyl)acrylamide to its trans isomer in the presence of an appropriate electron donor. Such isomerizing activity of these enzymes is much higher than their nitro-reducing activity. In addition, the cis-trans isomerization of some nitrofuran derivatives was demonstrated with the liver slices and the small intestines of rats. A new cis-trans isomerization mechanism which is based on transfer of a single electron by an enzyme system to a nitrofuran derivative to give the radical-anion was proposed. This postulated mechanism was supported by the preliminary experiments using pulse radiolysis technique.
mesh_terms: D000818:Animals; D008058:Dihydrolipoamide Dehydrogenase / Q000378:metabolism*; D004579:Electron Transport; D005609:Free Radicals; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D008956:Models, Chemical; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D009581:Nitrofurans; D011808:Quinone Reductases / Q000378:metabolism*; D051381:Rats; D013237:Stereoisomerism; D014969:Xanthine Oxidase / Q000378:metabolism*
chemical_list: D005609:Free Radicals; D009581:Nitrofurans; D014969:Xanthine Oxidase; D009247:NADH, NADPH Oxidoreductases; D011808:Quinone Reductases; D008058:Dihydrolipoamide Dehydrogenase