ISBN: 978-83-60043-10-3 - eurobic9

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Eurobic9, 2-6 September, 2008, Wrocław, Poland P119. Generation of NO by Xanthine Oxidase Family Enzymes L. Maia, R. Duarte, J. Moura REQUIMTE, Fac. Ciencias e Tecnologia, Univer. Nova de Lisboa, Depart. Química, C. Quimica Fina e Biotecnologia, 2829-516, Caparica, Portugal e-mail: lbmaia@dq.fct.unl.pt Xanthine oxidase (XO) is a homodimer, containing one molybdopterin, one FAD and two different [2Fe-2S] centres [1]. XO has a broad specificity for both reducing and oxidizing substrates. In addition to the well-known oxidation of hypoxanthine and xanthine, XO also catalyses the oxidation of a wide variety of aldehydes and nitrogen-containing heterocycles [2]. Much less known are nitrate and nitrite reductase activities related to XO [3-4], an reaction somewhat surprising due to the structural differences/similarities found between XO and bacterial nitrate reductases [5]. We investigate, in detail, the reduction of nitrate and nitrite to • NO by the bacterial (Desulfovibrio species) aldehyde oxidoreductase (AOR), one mononuclear molybdenum enzyme containing two different [2Fe-2S] centres, an enzyme of the XO family [6]. The present study examines the kinetics of • NO formation catalyzed by XO and by AOR, in the presence of dihydroxybenzaldehyde and benzaldehyde as reducing substrates. Anaerobic • NO formation was directly demonstrated using a • NO meter (ISO-NO TM ) and the • NO trap iron-N-methyl-D-glucamine dithiocarbamate, which in the presence of • NO gives rise to the characteristic EPR signal with g=2.04 and a N =12.7G. Additional EPR studies were performed to provide evidence for the sites of action of the substrates and the characteristic axial signals of the nitrosyl-iron complex were observed. Acknowledgement: L. Maia (SFRH/BPD/39036/2007) wishes to acknowledge to Fundacao para a Ciencia e a Tecnologia for financial support. References: [1] Hille, R., Nishino, T. (1995), FASEB J, 9, 995-1003. [2] Krenitsky, T.A., Neil, S.M., Elion, G.M., Hitchings, G.H. (1972), Arch. Biochem. Biophys., 150, 585-599. [3] Westerfield, W. W., Richert, D. A., Higgins, E. S. (1959), J. Biol. Chem., 234, 1897-1900. [4] Millar, T. M., Stevens, C. R., Benjamin, N., Eisenthal, R., Harrison, R., Blake, D. R. (1998), FEBS Lett., 427, 225-228. [5] González, P.J., Correia, C., Moura, I., Brondino, C.D., Moura, J.J.G. (2006), J. Inorg. Biochem., 100, 1015- 1023. [6] Brondino, C.D., Romao, M.J., Moura, I., Moura, J.J.G. (2006), Curr. Opin. Chem. Biol., 10, 109-114. _____________________________________________________________________ 238
Eurobic9, 2-6 September, 2008, Wrocław, Poland P120. Effect of DNA Modification by Platinum Complexes on Topoisomerase I Cleavage Activity J. Malina, V. Brabec Institute of Biophysics, AS CR, v.v.i., Kralovopolska 135, 612 65, Brno, Czech Republic e-mail: malina@ibp.cz Topoisomerase I (top 1) is ubiquitous and vital enzyme that participates in nearly all events related to DNA metabolism including replication, transcription and recombination. It is now viewed as important therapeutic target for cancer therapy and top 1 inhibitors, such as camptothecin or topotecan, are considered promising anticancer agents. In vitro experiments combining anticancer platinum drugs with top 1 poisons demonstrated synergistic activity in various human tumor cell lines. While the molecular mechanism of each of these agents is relatively well understood, the mode of action of these anticancer agents in combination is not clear. We studied influence of the DNA modification by selected platinum complexes on the activity of top 1 by gel electrophoresis on globally modified supercoiled plasmid DNA and short linear DNA fragment (161 bp). Further experiments were performed on DNA oligonucleotide (30 bp) containing specific adducts of platinum complexes in the close proximity to the cleavage site of top 1. The results show that the activity of top1 is inhibited by the presence of platinum adducts close to its cleavage site and that severe alteration in DNA structure is not necessary for inhibition to occur. It suggests that platinum adducts prevent top1 from recognizing its binding site and formation of top1-DNA cleavable complex. Acknowledgement: This research was supported by the Academy of Sciences of the Czech Republic (Grant B400040601). _____________________________________________________________________ 239
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ISBN: 978-83-60043-10-3 - eurobic9

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