António V. Xavier

New University of Lisbon, Lisboa, Lisbon, Portugal

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Publications (229)769.29 Total impact

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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 04/2010; 33(15). DOI:10.1002/chin.200215198
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    ABSTRACT: The fumarate reductases from S. frigidimarina NCIMB400 and S. oneidensis MR-1 are soluble and monomeric enzymes located in the periplasm of these bacteria. These proteins display two redox active domains, one containing four c-type hemes and another containing FAD at the catalytic site. This arrangement of single-electron redox co-factors leading to multiple-electron active sites is widespread in respiratory enzymes. To investigate the properties that allow a chain of single-electron co-factors to sustain the activity of a multi-electron catalytic site, redox titrations followed by NMR and visible spectroscopies were applied to determine the microscopic thermodynamic parameters of the hemes. The results show that the redox behaviour of these fumarate reductases is similar and dominated by a strong interaction between hemes II and III. This interaction facilitates a sequential transfer of two electrons from the heme domain to FAD via heme IV.
    Biochimica et Biophysica Acta (BBA) - Bioenergetics 02/2009; 1787(2-1787):113-120. DOI:10.1016/j.bbabio.2008.11.007 · 5.35 Impact Factor
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    ABSTRACT: Sulfate-reducing bacteria (SRB) are anaerobes readily found in oxic-anoxic interfaces. Multiple defense pathways against oxidative conditions were identified in these organisms and proposed to be differentially expressed under different concentrations of oxygen, contributing to their ability to survive oxic conditions. In this study, Desulfovibrio vulgaris Hildenborough cells were exposed to the highest concentration of oxygen that SRB are likely to encounter in natural habitats, and the global transcriptomic response was determined. Three hundred and seven genes were responsive, with cellular roles in energy metabolism, protein fate, cell envelope and regulatory functions, including multiple genes encoding heat shock proteins, peptidases and proteins with heat shock promoters. Of the oxygen reducing mechanisms of D. vulgaris only the periplasmic hydrogen-dependent mechanism was up-regulated, involving the [NiFeSe] hydrogenase, formate dehydrogenase(s) and the Hmc membrane complex. The oxidative defense response concentrated on damage repair by metal-free enzymes. These data, together with the down-regulation of the ferric uptake regulator operon, which restricts the availability of iron, and the lack of response of the peroxide-sensing regulator operon, suggest that a major effect of this oxygen stress is the inactivation and/or degradation of multiple metalloproteins present in D. vulgaris as a consequence of oxidative damage to their metal clusters.
    Archives of Microbiology 06/2008; 189(5):451-61. DOI:10.1007/s00203-007-0335-5 · 1.67 Impact Factor
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    ABSTRACT: Sulphate-reducing bacteria are important players in the global sulphur and carbon cycles, with considerable economical and ecological impact. However, the process of sulphate respiration is still incompletely understood. Several mechanisms of energy conservation have been proposed, but it is unclear how the different strategies contribute to the overall process. In order to obtain a deeper insight into the energy metabolism of sulphate-reducers whole-genome microarrays were used to compare the transcriptional response of Desulfovibrio vulgaris Hildenborough grown with hydrogen/sulphate, pyruvate/sulphate, pyruvate with limiting sulphate, and lactate/thiosulphate, relative to growth in lactate/sulphate. Growth with hydrogen/sulphate showed the largest number of differentially expressed genes and the largest changes in transcript levels. In this condition the most up-regulated energy metabolism genes were those coding for the periplasmic [NiFeSe] hydrogenase, followed by the Ech hydrogenase. The results also provide evidence for the involvement of formate cycling and the recently proposed ethanol pathway during growth in hydrogen. The pathway involving CO cycling is relevant during growth on lactate and pyruvate, but not during growth in hydrogen as the most down-regulated genes were those coding for the CO-induced hydrogenase. Growth on lactate/thiosulphate reveals a down-regulation of several energy metabolism genes similar to what was observed in the presence of nitrite. This study identifies the role of several proteins involved in the energy metabolism of D. vulgaris and highlights several novel genes related to this process, revealing a more complex bioenergetic metabolism than previously considered.
    Antonie van Leeuwenhoek 06/2008; 93(4):347-62. DOI:10.1007/s10482-007-9212-0 · 1.81 Impact Factor
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    ABSTRACT: The characterisation of individual centres in multihaem proteins is difficult due to the similarities in the redox and spectroscopic properties of the centres. NMR has been used successfully to distinguish redox centres and allow the determination of the microscopic thermodynamic parameters in several multihaem cytochromes c(3) isolated from different sulphate-reducing bacteria. In this article we show that it is also possible to discriminate the kinetic properties of individual centres in multihaem proteins, if the complete microscopic thermodynamic characterisation is available and the system displays fast intramolecular equilibration in the time scale of the kinetic experiment. The deconvolution of the kinetic traces using a model of thermodynamic control provides a reference rate constant for each haem that does not depend on driving force and can be related to structural factors. The thermodynamic characterisation of three tetrahaem cytochromes and their kinetics of reduction by sodium dithionite are reported in this paper. Thermodynamic and kinetic data were fitted simultaneously to a model to obtain microscopic reduction potentials, haem-haem and haem-proton interacting potentials, and reference rate constants for the haems. The kinetic information obtained for these cytochromes and recently published data for other multihaem cytochromes is discussed with respect to the structural factors that determine the reference rates. The accessibility for the reducing agent seems to play an important role in controlling the kinetic rates, although is clearly not the only factor.
    Biochimica et Biophysica Acta 10/2007; 1767(9):1169-79. DOI:10.1016/j.bbabio.2007.06.005 · 4.66 Impact Factor
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    ABSTRACT: Type I cytochrome c(3) is a key protein in the bioenergetic metabolism of Desulfovibrio spp., mediating electron transfer between periplasmic hydrogenase and multihaem cytochromes associated with membrane bound complexes, such as type II cytochrome c(3). This work presents the NMR assignment of the haem substituents in type I cytochrome c(3) isolated from Desulfovibrio africanus and the thermodynamic and kinetic characterisation of type I and type II cytochromes c(3) belonging to the same organism. It is shown that the redox properties of the two proteins allow electrons to be transferred between them in the physiologically relevant direction with the release of energised protons close to the membrane where they can be used by the ATP synthase.
    Biochimica et Biophysica Acta 03/2007; 1767(2):178-88. DOI:10.1016/j.bbabio.2007.01.012 · 4.66 Impact Factor
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    Inês A. C. Pereira · Miguel Teixeira · António V. Xavier ·
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    ABSTRACT: Hemeproteins are widespread in all groups of living organisms, both as components of key biological processes as well as in very specific metabolic pathways. By variation of either the heme porphyrin structure or the heme protein environment, the function and behavior of the hemeproteins may vary drastically, allowing its role in the most diverse processes. In this short review, selected examples of hemeproteins from anaerobes will be presented, aiming to show the basic, common features of these family of proteins, as well as their diversity in terms of function and composition.
    02/2007: pages 65-89;
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    ABSTRACT: Three membrane-bound redox complexes have been reported in Desulfovibrio spp., whose genes are not found in the genomes of other sulfate reducers such as Desulfotalea psycrophila and Archaeoglobus fulgidus. These complexes contain a periplasmic cytochrome c subunit of the cytochrome c(3) family, and their presence in these organisms probably correlates with the presence of a pool of periplasmic cytochromes c(3), also absent in the two other sulfate reducers. In this work we report the isolation and characterization of the first of such complexes, Tmc from D. vulgaris Hildenborough, which is associated with the tetraheme type II cytochrome c(3). The isolated Tmc complex contains four subunits, including the TpIIc(3) (TmcA), an integral membrane cytochrome b (TmcC), and two cytoplasmically predicted proteins, an iron-sulfur protein (TmcB) and a tryptophan-rich protein (TmcD). Spectroscopic studies indicate the presence of eight hemes c and two hemes b in the complex pointing to an alpha(2)betagammadelta composition (TmcA(2)BCD). EPR analysis reveals the presence of a [4Fe4S](3+) center and up to three other iron-sulfur centers in the cytoplasmic subunit. Nearly full reduction of the redox centers in the Tmc complex could be obtained upon incubation with hydrogenase/TpIc(3), supporting the role of this complex in transmembrane transfer of electrons resulting from periplasmic oxidation of hydrogen.
    Biochemistry 09/2006; 45(34):10359-67. DOI:10.1021/bi0610294 · 3.02 Impact Factor
  • António V. Xavier · José J. G. Moura · Isabel Moura ·
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    ABSTRACT: The main objective of this article is to put together the information available on the novel iron-sulfur centers and relate their properties with those of the iron-sulfur containing proteins. Special effort is put on the techniques used to identify their centers and in the discussion of the oxidation-reduction potentials involved.
    07/2006: pages 187-213;
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    Inês A. C. Pereira · António V. Xavier ·

    Encyclopedia of Inorganic Chemistry, 03/2006; , ISBN: 9780470862100
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    ABSTRACT: The NMR structure of the oxidised wild-type cytochrome c3 from Desulfovibrio vulgaris Hildenborough was determined in solution. Using a newly developed methodology, NMR data from the K45Q mutant was then grafted onto data from the wild-type protein to determine the structure in the region of the mutation. The structural origins of the redox-Bohr effect and haem-haem cooperativities are discussed with respect to the redox-related conformational changes observed in solution.
    Biochimica et Biophysica Acta 03/2006; 1757(2):143-53. DOI:10.1016/j.bbabio.2006.01.007 · 4.66 Impact Factor
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    ABSTRACT: Sulfate-reducing organisms use sulfate as an electron acceptor in an anaerobic respiratory process. Despite their ubiquitous occurrence, sulfate respiration is still poorly characterized. Genome analysis of sulfate-reducing organisms sequenced to date permitted the identification of only two strictly conserved membrane complexes. We report here the purification and characterization of one of these complexes, DsrMKJOP, from Desulfovibrio desulfuricans ATCC 27774. The complex has hemes of the c and b types and several iron-sulfur centers. The corresponding genes in the genome of Desulfovibrio vulgaris were analyzed. dsrM encodes an integral membrane cytochrome b; dsrK encodes a protein homologous to the HdrD subunit of heterodisulfide reductase; dsrJ encodes a triheme periplasmic cytochrome c; dsrO encodes a periplasmic FeS protein; and dsrM encodes another integral membrane protein. Sequence analysis and EPR studies indicate that DsrJ belongs to a novel family of multiheme cytochromes c and that its three hemes have different types of coordination, one bis-His, one His/Met, and the third a very unusual His/Cys coordination. The His/Cys-coordinated heme is only partially reduced by dithionite. About 40% of the hemes are reduced by menadiol, but no reduction is observed upon treatment with H2 and hydrogenase, irrespective of the presence of cytochrome c3. The aerobically isolated Dsr complex displays an EPR signal with similar characteristics to the catalytic [4Fe-4S]3+ species observed in heterodisulfide reductases. Further five different [4Fe-4S](2+/1+) centers are observed during a redox titration followed by EPR. The role of the DsrMKJOP complex in the sulfate respiratory chain of Desulfovibrio spp. is discussed.
    Biochemistry 02/2006; 45(1):249-62. DOI:10.1021/bi0515265 · 3.02 Impact Factor
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    ABSTRACT: The genome of Desulfovibrio vulgaris Hildenborough (DvH) encodes for six hydrogenases (Hases), making it an interesting organism to study the role of these proteins in sulphate respiration. In this work we address the role of the [NiFeSe] Hase, found to be the major Hase associated with the cytoplasmic membrane. The purified enzyme displays interesting catalytic properties, such as a very high H(2) production activity, which is dependent on the presence of phospholipids or detergent, and resistance to oxygen inactivation since it is isolated aerobically in a Ni(II) oxidation state. Evidence was obtained that the [NiFeSe] Hase is post-translationally modified to include a hydrophobic group bound to the N-terminal, which is responsible for its membrane association. Cleavage of this group originates a soluble, less active form of the enzyme. Sequence analysis shows that [NiFeSe] Hases from Desulfovibrionacae form a separate family from the [NiFe] enzymes of these organisms, and are more closely related to [NiFe] Hases from more distant bacterial species that have a medial [4Fe4S](2+/1+) cluster, but not a selenocysteine. The interaction of the [NiFeSe] Hase with periplasmic cytochromes was investigated and is similar to the [NiFe](1) Hase, with the Type I cytochrome c (3) as the preferred electron acceptor. A model of the DvH [NiFeSe] Hase was generated based on the structure of the Desulfomicrobium baculatum enzyme. The structures of the two [NiFeSe] Hases are compared with the structures of [NiFe] Hases, to evaluate the consensual structural differences between the two families. Several conserved residues close to the redox centres were identified, which may be relevant to the higher activity displayed by [NiFeSe] Hases.
    JBIC Journal of Biological Inorganic Chemistry 11/2005; 10(6):667-82. DOI:10.1007/s00775-005-0022-4 · 2.54 Impact Factor
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    ABSTRACT: Below 30 K, oxidized Desulfovibrio gigas hydrogenase presents an intense electron paramagnetic resonance (EPR) signal centered at g= 2.02, typical of an iron-sulfur center. In addition a rhombic EPR signal, attributed to Ni(III) species, is also observed [LeGall, J., Ljungdahl, P., Moura, I., Peck, H. D., Jr, Xavier, A. V., Moura, J. J. G., Teixeira, M., Huynh, B. H., and DerVartanian, D. V. (1982) Biochem. Biophys. Res. Commun. 106, 610–616; and Cammack, R., Patil, D., Aguirre, R., and Hatchikian, E. C., (1982) FEBS Lett. 142, 289–292]. At higher temperatures (77 K) the iron-sulfur EPR signal is broader and all the EPR features of the rhombic nickel signal can easily be observed. We have now obtained additional information concerning the redox properties of these EPR active centers, using an EPR redox titration method in the presence of dye mediators at pH = 8.5. The mid-point potential was determined to be - 70 mV for the Fe, S cluster and - 220 mV for the Ni center. Intermediate oxidation states were obtained upon partial reduction with either dithionite or hydrogen. Although upon dithionite reduction the centers are reduced in the order of decreasing mid-point reduction potentials, under a hydrogen atmosphere the nickel center reduces preferentially. This suggests a catalytic involvement of the nickel redox center in the binding of hydrogen. Preliminary Mössbauer studies on Desulfovibrio gigas hydrogenase reveal the presence of a paramagnetic 3 Fe center and two 4 Fe centers. The 3 Fe center is responsible for the g= 2.02 EPR signal but the two 4 Fe centers have been so far undetectable by EPR.
    03/2005; 130(3):481 - 484. DOI:10.1111/j.1432-1033.1983.tb07175.x
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    Liang CHEN · Ming-Yih LIU · Jean LEGALL · Paula FARELEIRA · Helena SANTOS · António V. XAVIER ·
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    ABSTRACT: An NADH–rubredoxin oxidoreductase previously isolated from Desulfovibrio gigas [LeGall, J. (1968) Ann. Inst. Pasteur 114, 109–115] has now been fully purified and further characterized. It contains two subunits of 27 kDa and 32 kDa. With two mid-point redox potentials of –295 mV and –325mV, this FMN- and FAD-containing protein can induce the specific reduction of D. gigas rubredoxin. In contrast, rubredoxins from the other Desulfovibrio species or desulforedoxin from D. gigas show very low reaction rates with the same enzyme. The phylogenetic significance of the narrow specificity of the enzyme toward the rubredoxin from the same organism is discussed. The purified enzyme has NADH oxidase activity with H2O2 as a final product of O2 reduction. The reaction is half-inhibited by 4.2μM p-chloromercuribenzoate, whereas cyanide and azide are not significant inhibitors in this reaction. The role of this protein as a part of the enzymic equipment that allows the formation of ATP in the presence of oxygen from the degradation of carbon reserves is discussed.
    03/2005; 216(2):443 - 448. DOI:10.1111/j.1432-1033.1993.tb18162.x
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    ABSTRACT: The 300-MHz proton NMR spectra of the tetrahaem cytochrome c3 from Desulfovibrio vulgaris were examined while varying the pH and the redox potential. The analysis of the complete NMR reoxidation pattern was done taking into account all the 16 redox states that can be present in the redox titration of a tetra-redox-center molecule. A network of saturation transfer experiments performed at different oxidation stages, between the fully reduced and the fully oxidized states, allowed the observation of different resonances for some of the haem methyl groups. In the present experimental conditions, some of the haems show a fast intramolecular electron exchange rate, but the intermolecular electron exchange is always slow. In intermediate reoxidation stages, large shifts of the resonances of some haem methyl groups were observed upon changing the pH. These shifts are discussed in terms of a pH dependence of the haem midpoint redox potentials. The physiological relevance of this pH dependence is discussed.
    03/2005; 127(1):151 - 155. DOI:10.1111/j.1432-1033.1982.tb06849.x
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    ABSTRACT: When purified, a high-potential c-type monohaem cytochrome from the nitrate-respiring organism, Wollinella succinogenes (VPI 10659), displayed a minimum molecular mass of 8.2 kDa and 0.9 mol iron and 0.95 mol haem groups/mol protein. Visible light spectroscopy suggested the presence of an equilibrium between-two ligand arrangements around the haem, i.e. an absorption band at 695 nm characteristic of haem-methionine coordination (low-spin form) coexisting with a high-spin form revealed by a band at 619 nm and a shoulder at 498 nm. The mid-point redox potential measured by visible redox titration of the low-spin form was approximately +100 mV. Binding cyanide (Ka= 5 × 105 M−1) resulted in the displacement of the methionyl axial residue, and full conversion to a low-spin, cyanide-bound form.Structural features were studied by 300-MHz 1H-NMR spectroscopy. In the oxidized state, the pH dependence of the haem methyl resonances (pH range 5–10) and the magnetic susceptibility measurements (using an NMR method) were consistent with the visible light spectroscopic data for the presence of a high-spin/low-spin equilibrium with a transition pKa of 7.3. The spin equilibrium was fast on the NMR time scale. The haem methyl resonances presented large downfield chemical shifts. An unusually broad methyl resonance at around 35 ppm (pH = 7.5, 25°C) was extremely temperature-dependent [δ(323K) –δ(273K) = 7.2 ppm] and was assigned to the S-CH3 group of the axial methionine. In the ferrous state only a low-spin form is present. The haem meso protons, the methyl group and the methylene protons from the axial methionine were identified in the reduced form. The resonances from the aromatic residues (three tyrosines and one phenylalanine) were also assigned.Detailed monitoring of the NMR-redox pattern of the monohaem cytochrome from the fully reduced up to the fully oxidized state revealed that the rate of the intermolecular electronic exchange process was approximately 6 × 106 M−1 s−1 at 303 K and pH = 6.31.A dihaem cytochrome also present in the crude cell extract and purified to a homogeneous state, exhibited a molecular mass of 11 kDa and contained 2.43 mol iron and 1.89 mol haem c moieties/mol cytochrome. The absorption spectrum in the visible region exhibited no band at 695 nm, suggesting that methione is not a ligand for either of the two haems. Recovery of only small amounts of this protein prevented more detailed structural analyzes.
    03/2005; 177(3):673 - 682.
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    ABSTRACT: Flavocytochrome c3 from Shewanella frigidimarina (fcc3) is a tetrahaem periplasmic protein of 64 kDa with fumarate reductase activity. This work reports the first example of NMR techniques applied to the assignment of the thermodynamic order of oxidation of the four individual haems for such large protein, expanding its applicability to a wide range of proteins. NMR data from partially and fully oxidised samples of fcc3 and a mutated protein with an axial ligand of haem IV replaced by alanine were compared with calculated chemical shifts, allowing the structural assignment of the signals and the unequivocal determination of the order of oxidation of the haems. As oxidation progresses the fcc3 haem domain is polarised, with haems I and II much more oxidised than haems III and IV, haem IV being the most reduced. Thus, during catalysis as an electron is taken by the flavin adenosine dinucleotide from haem IV, haem III is eager to re-reduce haem IV, allowing the transfer of two electrons to the active site.
    FEBS Letters 01/2005; 578(1-2):185-90. DOI:10.1016/j.febslet.2004.10.098 · 3.17 Impact Factor
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    ABSTRACT: The tetraheme cytochrome c3 isolated from Desulfomicrobium baculatum (DSM 1743)(Dsmb) was cloned, and the sequence analysis showed that this cytochrome differs in just three amino acid residues from the cytochrome c3 isolated from Desulfomicrobium norvegicum (Dsmn): (DsmnXXDsmb) Thr-37 --> Ser, Val-45 --> Ala, and Phe-88 --> Tyr. X-ray crystallography was used to determine the structure of cytochrome c3 from Dsmb, showing that it is very similar to the published structure of cytochrome c3 from Dsmn. A detailed thermodynamic and kinetic characterization of these two tetraheme cytochromes c3 was performed by using NMR and visible spectroscopy. The results obtained show that the network of cooperativities between the redox and protonic centers is consistent with a synergetic process to stimulate the hydrogen uptake activity of hydrogenase. This is achieved by increasing the affinity of the cytochrome for protons through binding electrons and, reciprocally, by favoring a concerted two-electron transfer assisted by the binding of proton(s). The data were analyzed within the framework of the differences in the primary and tertiary structures of the two proteins, showing that residue 88, close to heme I, is the main cause for the differences in the microscopic thermodynamic parameters obtained for these two cytochromes c3. This comparison reveals how replacement of a single amino acid can tune the functional properties of energy-transducing proteins, so that they can be optimized to suit the bioenergetic constraints of specific habitats.
    Journal of Biological Chemistry 12/2004; 279(50):52227-37. DOI:10.1074/jbc.M408763200 · 4.57 Impact Factor
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    António V Xavier ·
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    ABSTRACT: Cooperative effects are fundamental for electroprotonic energy transduction processes, crucial to sustain much of life chemistry. However, the primary cooperative mechanism by which transmembrane proteins couple the downhill transfer of electrons to the uphill activation (acidification) of protic groups is still a matter of great controversy. To understand cooperative processes fully, it is necessary to obtain the microscopic thermodynamic parameters of the functional centres and relate them to the relevant structural features, a task difficult to achieve for large proteins. The approach discussed here explores how this may be done by extrapolation from mechanisms used by simpler proteins operative in similar processes. The detailed study of small, soluble cytochromes performing electroprotonic activation has shown how they use anti-electrostatic effects to control the synchronous movement of charges. These include negative e(-)/H(+) (redox-Bohr effect) cooperativities. This capacity is the basis to discuss an unorthodox mechanism consistent with the available experimental data on the process of electroprotonic energy transduction performed by cytochrome c oxidase (CcO).
    Biochimica et Biophysica Acta 08/2004; 1658(1-2):23-30. DOI:10.1016/j.bbabio.2004.03.017 · 4.66 Impact Factor

Publication Stats

7k Citations
769.29 Total Impact Points


  • 1986-2010
    • New University of Lisbon
      • • Institute of Chemical and Biological Technology (ITQB)
      • • Faculty of Sciences and Technology
      Lisboa, Lisbon, Portugal
  • 1976-2005
    • University of Lisbon
      Lisboa, Lisbon, Portugal
  • 1974-2005
    • Instituto Técnico y Cultural
      Santa Clara de Portugal, Michoacán, Mexico
  • 2004
    • Universidade da Beira Interior
      Ковильян, Castelo Branco, Portugal
  • 2002
    • Instituto de Química Avanzada
      Barcino, Catalonia, Spain
  • 1982-1999
    • University of Georgia
      • • Department of Biochemistry and Molecular Biology
      • • Department of Microbiology
      Атина, Georgia, United States
    • University of Minnesota Duluth
      Duluth, Minnesota, United States
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 1995
    • University of Southampton
      • Division of Chemistry
      Southampton, England, United Kingdom
  • 1991
    • University of Camerino
      Camerino, The Marches, Italy
  • 1988
    • Emory University
      • Department of Physics
      Atlanta, Georgia, United States
  • 1972-1974
    • University of Oxford
      • Inorganic Chemistry Laboratory
      Oxford, England, United Kingdom