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

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.
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