http://hdl.handle.net/10362/2111 2013-06-19T16:58:55Z 2013-06-19T16:58:55Z Batista, Ana P. http://hdl.handle.net/10362/5160 2011-02-16T18:03:27Z 2010-09-01T00:00:00Z

Title: Energy transduction by respiratory complex I Authors: Batista, Ana P. Abstract: The aim of the work presented in this dissertation was to provide a contribution to the understanding of the energy transducing mechanism of respiratory complex I. This enzyme is present in most bacteria and in all mitochondrial systems and it is characterized by its large number of subunits, its prosthetic groups (flavin and iron-sulfur centers), and its NADH:quinone oxidoreductase activity sensitive to specific inhibitors and coupled with charge translocation across the membrane.(...) Description: Dissertation presented to obtain a PhD degree in Biochemistry at the Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa

2010-09-01T00:00:00Z Refojo, Patrícia N. http://hdl.handle.net/10362/5159 2011-02-16T17:55:24Z 2010-07-01T00:00:00Z

Title: The alternative complex III from Rhodothermus marinus - a prototype of a new family of quinol: electron acceptor oxidoreductase Authors: Refojo, Patrícia N. Abstract: The aim of the work presented in this thesis was the characterization of a complex with quinol: electron carrier oxidodoreductase activity present in the membranes of the thermohalophilic bacterium Rhodothermus (R.) marinus. The complexes involved in the R. marinus respiratory chain have been extensively studied in the past few years. Specifically, the purification and characterization of a complex I (NADH: quinone oxidoreductase), a complex II (succinate:quinone oxidoreductase) and of three different oxygen reductases from the heme-copper oxygen reductases superfamily have been performed. Since those oxygen reductases are unable to receive electrons from quinol molecules, the presence of a complex linking complexes I and II to the oxygen reductases was needed. In fact, a complex with quinol: HiPIP oxidoreductase activity was purified and partially characterized. The absence of the Rieske protein indicated that the complex isolated from R. marinus has a different composition when compared with the typical cytochrome bc1 complex.(...) Description: Dissertation presented to obtain a PhD degree in Biochemistry at the Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa

2010-07-01T00:00:00Z Romão, Célia V. Pereira, Inês C. Xavier, António V.; LeGall, Jean Teixeira, Miguel http://hdl.handle.net/10362/4758 2011-08-06T00:01:19Z 1997-01-01T00:00:00Z

Title: Characterization of the [NiFe] Hydrogenase from the sulfate reducer Desulfovibrio vulgaris Hildenborough Authors: Romão, Célia V.; Pereira, Inês C.; Xavier, António V.;; LeGall, Jean; Teixeira, Miguel Abstract: The [NiFe] hydrogenase from Desulfovibrio vulgaris Hildenborough was isolated from the cytoplasmic membranes and characterized by EPR spectroscopy. It has a total molecular mass of 98.7 kDa (subunits of 66.4 and 32.3 kDa), and contains 1 nickel and 12 Fe atoms per heterodimer. The catalytic activities for hydrogen consumption and production were determined to be 174 and 89 umol H2 min-1 mg -1, respectively. As isolated, under aerobic conditions, this hydrogenase exhibits EPR signals characteristic of the nickel centers in [NiFe] hydrogenases (Ni-A signal at gx,y,z=2.32, 2.23 and ~2.0 and Ni-B signal at gx,y,z=2.33, 2.16 and ~2.0) as well as an intense quasi-isotropic signal centered at g=2.02 due to the oxidized [3Fe-4S] center. The redox profile under hydrogen atmosphere is remarkably similar to that of other [NiFe] hydrogenases. The signals observed for the oxidized state disappear, first being substituted by the Ni-C type signal (gx,y,z=2.19, 2.14, ~2.01), which upon long incubation under hydrogen yields the split Ni-C signal due to interaction with the reduced [4Fe-4S] centers.

1997-01-01T00:00:00Z Gomes, Claudio Vicente, João Wasserfallen, Alain Teixeira, Miguel http://hdl.handle.net/10362/3584 2010-05-21T10:24:57Z 1999-01-01T00:00:00Z

Title: Spectroscopic Studies and Characterization of a Novel Electron-Transfer Chain Authors: Gomes, Claudio; Vicente, João; Wasserfallen, Alain; Teixeira, Miguel Abstract: A novel two-component enzyme system from Escherichia coli involving a flavorubredoxin (FlRd) and its reductase was studied in terms of spectroscopic, redox, and biochemical properties of its constituents. FlRd contains one FMN and one rubredoxin (Rd) center per monomer. To assess the role of the Rd domain, FlRd and a truncated form lacking the Rd domain (FlRd¢Rd), were characterized. FlRd contains 2.9 ( 0.5 iron atoms/subunit, whereas FlRd¢Rd contains 2.1 ( 0.6 iron atoms/subunit. While for FlRd one iron atom corresponds to the Rd center, the other two irons, also present in FlRd¢Rd, are most probably due to a di-iron site. Redox titrations of FlRd using EPR and visible spectroscopies allowed us to determine that the Rd site has a reduction potential of -140 ( 15 mV, whereas the FMN undergoes reduction via a red-semiquinone, at -140 ( 15 mV (Flox/Flsq) and -180 ( 15 mV (Flsq/Flred), at pH 7.6. The Rd site has the lowest potential ever reported for a Rd center, which may be correlated with specific amino acid substitutions close to both cysteine clusters. The gene adjacent to that encoding FlRd was found to code for an FAD-containing protein, (flavo)rubredoxin reductase (FlRd-reductase), which is capable of mediating electron transfer from NADH to DesulfoVibrio gigas Rd as well as to E. coli FlRd. Furthermore, electron donation was found to proceed through the Rd domain of FlRd as the Rd-truncated protein does not react with FlRd-reductase. In vitro, this pathway links NADH oxidation with dioxygen reduction. The possible function of this chain is discussed considering the presence of FlRd homologues in all known genomes of anaerobes and facultative aerobes.

1999-01-01T00:00:00Z