NITROREDUCTASE REACTIONS OF ARABIDOPSIS-THALIANA THIOREDOXIN REDUCTASE

Citation
V. Miskiniene et al., NITROREDUCTASE REACTIONS OF ARABIDOPSIS-THALIANA THIOREDOXIN REDUCTASE, Biochimica et biophysica acta. Bioenergetics, 1366(3), 1998, pp. 275-283
Citations number
41
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Biology,Biophysics
ISSN journal
0005-2728
Volume
1366
Issue
3
Year of publication
1998
Pages
275 - 283
Database
ISI
SICI code
0005-2728(1998)1366:3<275:NROATR>2.0.ZU;2-3
Abstract
Arabidopsis thaliana NADPH:thioredoxin reductase (TR, EC 1.6.4.5) cata lyzed redox cycling of aromatic nitrocompounds, including the explosiv es 2,4,6-trinitrotoluene and tetryl, and the herbicide 3,5-dinitro-o-c resol. The yield of nitro anion radicals was equal to 70-90%, Redox cy cling of tetryl was accompanied by formation of N-methylpicramide. Bim olecular rate constants of nitroaromatic reduction (k(cat)/K-m) and re action catalytic constants (k(cat)) increased upon an increase in oxid ant single-electron reduction potential (E-7(1)). Using the compounds with an unknown E-7(1) value, the reactivity of TR increased parallell y to the increase in reactivity of ferredoxin:NADP(+) reductase of Ana baena PCC 7119 (EC 1.18.1.2). This indicated that the main factor dete rmining reactivity of nitroaromatics towards TR was their energetics o f single-electron reduction. Incubation of reduced TR in the presence of tetryl or 2,4-dinitrochlorobenzene resulted in a loss of thioredoxi n reductase activity, most probably due to modification of reduced cat alytic disulfide, whereas nitroreductase reaction rates were unchanged . This means that on the analogy of quinone reduction by TR (D. Birona ite, Z. Anusevicius, J.-P. Jacquot, N. Cenas, Biochim. Biophys. Acta 1 383 (1998) 82-92), FAD and not catalytic disulfide of TR was responsib le for the reduction of nitroaromatics. Tetryl, 2,4,6-trinitrotoluene and thioredoxin increased the FAD fluorescence intensity of TR. This f inding suggests that nitroaromatics may bind close to the thioredoxin- binding site at the catalytic disulfide domain of TR, and induce a con formational change of enzymes (S.B. Mulrooney, C.H. Williams Jr., Prot ein Sci. 6 (1997) 2188-2195). Our data indicate that certain nitroarom atic herbicides, explosives and other classes of xenobiotics may inter fere with the reduction of thioredoxin by plant TR, and confer prooxid ant properties to this antioxidant enzyme. (C) 1998 Elsevier Science B .V. All rights reserved.