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

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Eurobic9, 2-6 September, 2008, Wrocław, Poland H. Sigel P181. Metal Ion-Binding Properties of Two Isomeric Uracilmethylphosphonates Department of Chemistry, Inorganic Chemistry, University of Basel, Spitalstrasse 51, CH-4056, BASEL, Switzerland e-mail: helmut.sigel@unibas.ch The uracilmethylphosphonates, 5Umpa 2– = uracil(5)-CH2-PO3 2– and 6Umpa 2– = uracil(6)-CH2-PO3 2– , show interesting pharmacological properties [1] and they fit thus into a series of artificial acyclic nucleotide analogues, a wellknown member in use in hepatitis B therapy is Adefovir = PMEA 2– = adenine(9)-CH2CH2-O-CH2-PO3 2– [2]. Since the action of such phosphonates involves metal ions [2], we studied the M 2+ -binding properties of 5/6Umpa 2– in aq. solution [3]. In both cases mainly the phosphonate group determines the stability of the M(Umpa) complexes (M 2+ = Mg 2+ , Ca 2+ , Cu 2+ , Zn 2+ , Cd 2+ ). However, for M(5Umpa) with Cu 2+ , Zn 2+ or Cd 2+ an increased stability is observed, which, based on steric considerations, must be attributed to a 7-membered chelate formed by the phosphonate-coordinated M 2+ with the oxygen of (C4)O. The formation degree of the M(5Umpa) chelates varies with the metal ion involved; e.g., for Mg 2+ , Cu 2+ and Zn 2+ it is ca. 0, 46 and 26%, respectively. Of course, the (C4)O interaction facilitates deprotonation of (N3)H giving thus also rise to a larger formation degree of the chelates (up to 90%) in the M(5Umpa – H) – species. For uracil the (N3) – /(N1) – ratio is about 80/20 [4], showing that (N1)H is only a bit less acidic than (N3)H. Indeed, the M(6Umpa) complexes undergo (N1)H deprotonation at physiological pH forming 6-membered M(6Umpa – H) – chelates with high formation degrees [3]. Acknowledgements:Supported by the Department of Chemistry, University of Basel, Switzerland. References: [1] J. Ochocki, J. Graczyk, Pharmazie 53 (1998) 884–885. [2] H. Sigel, Chem. Soc. Rev. 33 (2004) 191–200. [3] E. Freisinger, R. Griesser, B. Lippert, C.F. Moreno-Luque, J. Niclós-Gutiérrez, J. Ochocki, B.P. Operschall, H. Sigel, submitted. [4] C.F. Moreno-Luque, E. Freisinger, B. Costisella, R. Griesser, J. Ochocki, B. Lippert, H. Sigel, J. Chem. Soc., Perkin Trans 2 (2001) 2005–2011. _____________________________________________________________________ 300
Eurobic9, 2-6 September, 2008, Wrocław, Poland P182. Kinetic Studies on the Multihemic Nitrite Reductase from Desulfovibrio desulfuricans ATCC 27774 C.M. Silveira a , S. Besson a, b , J.J.G. Moura a , M. Gabriela Almeida a REQUIMTE - Departamento de Química, CQFB, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal b UIBD, Faculdade de Engenharia e Ciências Naturais, Universidade Lusófona de Humanidades e Tecnologias, Campo Grande 376, 1749-024 Lisboa, Portugal c Escola Superior de Saúde Egas Moniz, Monte de Caparica, 2829-511 Caparica, Portugal e-mail: celia.silveira@dq.fct.unl.pt The multiheme nitrite reductase (ccNiR) from the δ-proteobacterium Desulfovibrio desulfuricans ATCC 27774 is able to reduce nitrite to ammonia in a six-electron transfer reaction. Though, low activities have also been reported for the reduction of hydroxylamine, nitric oxide and sulphite [1]. ccNiR is a membrane associated complex composed of two subunits NrfA and NrfH, apparently following a α4β2 architecture [2]. Although extensively characterized from the spectroscopic, biochemical and structural points of view, most of ccNiR’s kinetic characteristics are still unknown. Due to its high specific activity towards nitrite, ccNiR has been targeted for biosensor applications using different electronic mediators for signal transduction. As a result, a set of kinetic data concerning the immobilized protein was obtained [3-5]. In this work the homogeneous kinetic behaviour of ccNiR is being evaluated in the presence of several redox mediators (methyl viologen, diquat, phenosafranine, anthraquinone-sulfonate). Enzyme activities were measured by a continuous method following the mediator reoxidation, and by a discrete manner, titrating nitrite and ammonia at regular time intervals. Regardless the redox potential of the electron donor, ammonium was always the main product. Among the tested mediators, methyl viologen showed the highest turnover number. The kcat and KM values for both nitrite and mediator were influenced by the incubation temperature. Acknowledgements: The authors thank the financial support funded by REQUIMTE and Fundação para a Ciência e Tecnologia (POCI/QUI/58026/2004 and SFRH/BD/28921/2006). References: [1] Stach P. et al, J. Inorg. Biochem., 2000, 79(1-4), 381-385. [2] Rodrigues M.L. et al, EMBO J., 2006, 25(24), 5951–5960. [3] Strehlitz B. et al, Anal. Chem., 1996, 68, 807-816. [4] Almeida M.G. et al, Biosens. Bioelectron., 2007, 22(11), 2485-2492. [5] Chen H. et al, Electrochem. Comm., 2007, 9, 2241–2246. _____________________________________________________________________ 301 a, c
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ISBN: 978-83-60043-10-3 - eurobic9

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