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Redox states of cytochrome c3 in the absence and presence of ferredoxin, Moura, J. J., Xavier A. V., Cookson D. J., Moore G. R., and Williams R. J. , FEBS Lett, Sep 15, Volume 81, Number 2, p.275-80, (1977) AbstractWebsite
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Oxidation-reduction studies of the Mo-(2Fe-2S) protein from Desulfovibrio gigas, Moura, J. J., Xavier A. V., Cammack R., Hall D. O., Bruschi M., and Legall J. , Biochem J, Aug 1, Volume 173, Number 2, p.419-25, (1978) AbstractWebsite

Potentiometric titration followed by e.p.r. measurements were used to determine the midpoint reduction potentials of the redox centres of a molybdenum-containing iron-sulphur protein previously isolated from Desulfovibrio gigas, a sulphate-reducing bacterium (Moura, Xavier, Bruschi, Le Gall, Hall & Cammack (1976) Biochem. Biophys. Res. Commun. 728 782-789; Moura, Xavier, Bruschi, Le Gall & Cabral (1977) J. Less Common Metals 54, 555-562). The iron-sulphur centres could readily be distinguished into three types by means of g values, temperature effect, oxidation-reduction potential values and reduction rates. The type-I Fe-S centres are observed at 77 K. They show mid-point potential values of -260mV (Fe-S type IA) and -440 mV (Fe-S type IB). Centres of types IA and IB appear to have similar spectra at 77 K and 24 K. The Fe-S type-II centres are only observed below 65 K and have a midpoint potential of -28mV. Long equilibration times (30 min) with dye mediators under reducing conditions were necessary to observe the very slow equilibrating molybdenum signals. The potential values associated with this signal were estimated to be approx. -415 mV for Mo(VI)/Mo(V) and-530mV for Mo(V)/Mo(IV).

Unambiguous identification of the nickel EPR signal in 61Ni-enriched Desulfovibrio gigas hydrogenase, Moura, J. J., Moura I., Huynh B. H., Kruger H. J., Teixeira M., DuVarney R. C., Dervartanian D. V., Xavier A. V., Peck, H. D. Jr., and Legall J. , Biochem Biophys Res Commun, Oct 29, Volume 108, Number 4, p.1388-93, (1982) AbstractWebsite
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Structural aspects of denitrifying enzymes, Moura, I., and Moura J. J. , Curr Opin Chem Biol, Apr, Volume 5, Number 2, p.168-75, (2001) AbstractWebsite

The reduction of nitrate to nitrogen gas via nitrite, nitric oxide and nitrous oxide is the metabolic pathway usually known as denitrification, a key step in the nitrogen cycle. As observed for other elemental cycles, a battery of enzymes are utilized, namely the reductases for nitrate, nitrite, nitric oxide and nitrous oxide, as well as multiple electron donors that interact with these enzymes, in order to carry out the stepwise reactions that involve key intermediates. Because of the importance of this pathway (of parallel importance to the nitrogen-fixation pathway), efforts are underway to understand the structures of the participating enzymes and to uncover mechanistic aspects. Three-dimensional structures have been solved for the majority of these enzymes in the past few years, revealing the architecture of the active metal sites as well as global structural aspects, and possible mechanistic aspects. In addition, the recognition of specific electron-transfer partners raises important questions regarding specific electron-transfer pathways, partner recognition and control of metabolism.

EPR and Mossbauer studies of desulforedoxin from Desulfovibrio gigas, Moura, I., Huynh B., Legall J., Xavier A. V., and Munck E. , Ciênc. Biol. (Portugal), Volume 5, p.199-201, (1980) Abstract
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NMR redox studies of Desulfovibrio vulgaris Cytochrome c3. Electron transfer mechanisms, Moura, J. J., Santos H., Moura I., Legall J., Moore G. R., Williams R. J., and Xavier A. V. , Eur J Biochem, Sep, Volume 127, Number 1, p.151-5, (1982) AbstractWebsite

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.

Influence of storage solution on enamel demineralization submitted to pH cycling, Moura, J. S., Rodrigues L. K., Del Bel Cury A. A., Lima E. M., and Garcia R. M. , J Appl Oral Sci, Sep, Volume 12, Number 3, p.205-8, (2004) AbstractWebsite

Extracted human teeth are frequently used for research or educational purposes. Therefore, it is necessary to store them in disinfectant solutions that do not alter dental structures. Thus, this study evaluated the influence of storage solution on enamel demineralization. For that purpose, sixty samples were divided into the following groups: enamel stored in formaldehyde (F1), stored in thymol (T1), stored in formaldehyde and submitted to pH cycling (F2), stored in thymol and submitted to pH cycling (T2). All samples were evaluated by cross-sectional microhardness analysis and had their percentage of mineral volume versus micrometer (integrated area) determined. Differences between groups were found up to 30-microm depth from the enamel surface (p < 0.05), where samples from group T2 were more demineralized. It was concluded that the storage solution influenced the reaction of a dental substrate to a cariogenic challenge, suggesting that formaldehyde may increase enamel resistance to demineralization, when compared to demineralization occurring in enamel stored in thymol solution.

A cobalt containing protein isolated from Desulfovibrio gigas, a sulfate reducer, Moura, J. J., Moura I., Bruschi M., Legall J., and Xavier A. V. , Biochem Biophys Res Commun, Feb 12, Volume 92, Number 3, p.962-70, (1980) AbstractWebsite
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Nuclear-magnetic-resonance studies of Desulfuromonas acetoxidans cytochrome c551.5 (c7), Moura, J. G., Moore G. R., Williams R. J., Probst I., Legall J., and Xavier A. V. , Eur J Biochem, Nov 2, Volume 144, Number 3, p.433-40, (1984) AbstractWebsite

1H nuclear magnetic resonance (NMR) spectroscopy has been used to examine cytochrome c551.5 (c7) from the sulfur reducer, Desulfuromonas acetoxidans. This protein contains three hemes. Two stable oxidation states (the fully oxidized and the fully reduced) as well as intermediate oxidation states were studied. The axial ligands of the iron were found to be neutral histidines. The redox properties of cytochrome c7 were examined and good quantitative agreement found between the NMR results and previously reported redox potential measurements. The properties of cytochrome c7 are discussed together with those of the homologous tetraheme cytochromes c3 isolate from sulfate-reducing bacteria.

Simple and Complex Iron-Sulfur Proteins in Sulfate Reducing Bacteria, Moura, Isabel, Pereira Alice S., Tavares Pedro, and Moura José J. G. , Advances in Inorganic Chemistry, Volume Volume 47, p.361-419, (1999) Abstract
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Characterization of two dissimilatory sulfite reductases (desulforubidin and desulfoviridin) from the sulfate-reducing bacteria. Moessbauer and EPR studies, Moura, I., Legall J., Lino A. R., Peck H. D., Fauque G., Xavier A. V., Dervartanian D. V., Moura J. J. G., and Huynh B. H. , Journal of the American Chemical Society, 1988/02/17, Volume 110, Number 4, p.1075-1082, (1988) AbstractWebsite
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Nickel - a redox catalytic site in hydrogenase, Moura, J. J. G., Teixeira M., Moura I., Xavier A. V., and Legall J. , Journal of Molecular Catalysis, Volume 23, Number 2–3, p.303-314, (1984) AbstractWebsite
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[15] Characterization of three proteins containing multiple iron sites: Rubrerythrin, desulfoferrodoxin, and a protein containing a six-iron cluster, Moura, Isabel, Tavares Pedro, and Ravi Natarajan , Methods in Enzymology, Volume Volume 243, p.216-240, (1994) Abstract
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NICKEL-CONTAINING HYDROGENASES, Moura, J. J. G., Moura I., Teixeira M., Xavier A. V., Fauque G. D., and Legall J. , Metal Ions in Biological Systems, 1988, Volume 23, p.285-314, (1988) AbstractWebsite
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NMR characterization of three forms of ferredoxin from Desulphovibrio gigas, a sulphate reducer, Moura, J. J., Xavier A. V., Bruschi M., and Gall J. L. , Biochim Biophys Acta, Feb 7, Volume 459, Number 2, p.278-89, (1977) AbstractWebsite

A NMR and magnetic susceptibility study of the oxidized and reduced states of three different oligomers (forms) of a [4Fe-4S] ferrodoxin protein from Desulphovibrio gigas, FdI, FdI', and FdII was carried out. FdI and FdI' are different trimers and FdII a tetramer of the same basic subunit. A probable assignment of the contact shifted resonances is indicated. Since the temperature dependences of the contact shifted responances associated with each [4Fe-4S] are not all similar a delocalized model for the spin densities on the 4Fe does not apply. The exchange rate between oxidized and reduced states is slow on the NMR time scale. The three oligomers are not magnetically equivalent. Using the "three state hypothesis" terminology it is shown that FdIox is predominantly in the C2- state and changes upon reduction into the C3- state, while FdIIox is in the C- state and changes into the C2- state. FdI' does not easily fit into this classification. This study shows a similarity of magnetic behaviour between FdI and bacterial ferredoxins (e.g. Bacillus polymyxa) and between FdII and HiPIP from Chromatium sp. The influence of the quaternary structure on the stabilization of the different oxidation states of ferredoxins as well as on their redox potentials is discussed.

Purification and characterization of desulfoferrodoxin. A novel protein from Desulfovibrio desulfuricans (ATCC 27774) and from Desulfovibrio vulgaris (strain Hildenborough) that contains a distorted rubredoxin center and a mononuclear ferrous center, Moura, I., Tavares P., Moura J. J., Ravi N., Huynh B. H., Liu M. Y., and Legall J. , J Biol Chem, Dec 15, Volume 265, Number 35, p.21596-602, (1990) AbstractWebsite

A new type of non-heme iron protein was purified to homogeneity from extracts of Desulfovibrio desulfuricans (ATCC 27774) and Desulfovibrio vulgaris (strain Hildenborough). This protein is a monomer of 16-kDa containing two iron atoms per molecule. The visible spectrum has maxima at 495, 368, and 279 nm and the EPR spectrum of the native form shows resonances at g = 7.7, 5.7, 4.1 and 1.8 characteristic of a high-spin ferric ion (S = 5/2) with E/D = 0.08. Mossbauer data indicates the presence of two types of iron: an FeS4 site very similar to that found in desulforedoxin from Desulfovibrio gigas and an octahedral coordinated high-spin ferrous site most probably with nitrogen/oxygen-containing ligands. Due to this rather unusual combination of active centers, this novel protein is named desulfoferrodoxin. Based on NH2-terminal amino acid sequence determined so far, the desulfoferrodoxin isolated from D. desulfuricans (ATCC 27774) appears to be a close analogue to a recently discovered gene product from D. vulgaris (Brumlik, M.J., and Voordouw, G. (1989) J. Bacteriol. 171, 49996-50004), which was suggested to be a rubredoxin oxidoreductase. However, reduced pyridine nucleotides failed to reduce the desulforedoxin-like center of this new protein.

A comparative spectroscopic study of two non-haem iron proteins lacking labile sulphide from Desulphovibrio gigas, Moura, I., Xavier A. V., Cammack R., Bruschi M., and Legall J. , Biochimica et Biophysica Acta (BBA) - Protein Structure, Volume 533, Number 1, p.156-162, (1978) AbstractWebsite
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Ferredoxin from Methanosarcina barkeri: evidence for the presence of a three-iron center, Moura, I., Moura J. J., Huynh B. H., Santos H., Legall J., and Xavier A. V. , Eur J Biochem, Aug, Volume 126, Number 1, p.95-8, (1982) AbstractWebsite

Methanosarcina barkeri ferredoxin was purified and characterized by electron paramagnetic resonance (EPR) and Mossbauer spectroscopy. The purification procedure included chromatographic steps on DEAE-cellulose and gel filtration. The isolated protein is unstable under aerobic conditions. The ferredoxin exhibits charge transfer bands at 283 nm and 405 nm with an absorption ratio A405/A283 = 0.73. Its molecular weight has been estimated to be 20000-22000 by gel filtration chromatography. The native ferredoxin exhibits an intense EPR signal at g = 2.02 and only a very weak g = 1.94 signal develops upon reduction with dithionite. The Mossbauer spectra of the reduced protein are characteristic of a [3Fe-3S] center. The combined EPR and Mossbauer studies show that M. barkeri ferredoxin contains only [3Fe-3S] clusters, similar to Azotobacter vinelandii Fd[Emptage, M.H., Kent, T.A., Huynh, B.H., Rawlings, J., Orme-Johnson, W.H. & Munck, M. (1980) J. Biol. Chem. 255, 1793-1796], Desulfovibrio gigas FdII [Huynh, B.H., Moura, J.J.G., Moura, I., Kent, T.A., LeGall, J., Xavier, A.V. & Munck, E. (1980) J. Biol. Chem. 255, 3242-3244] and mitochondrial beef heart aconitase [Kent, T.A., Dreyer, J.-L., Kennedy, M.C., Huynh, B.H., Emptage, M.H., Beinert, H. & Munck, E. (1982) Proc. Natl Acad. Sci. USA, 79, 1096-1100].

Nitrate and nitrite utilization in sulfate-reducing bacteria, Moura, I., Bursakov S., Costa C., and Moura J. J. , Anaerobe, Oct, Volume 3, Number 5, p.279-90, (1997) AbstractWebsite
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Structural and functional approach toward a classification of the complex cytochrome c system found in sulfate-reducing bacteria, Moura, J. J., Costa C., Liu M. Y., Moura I., and Legall J. , Biochim Biophys Acta, May 23, Volume 1058, Number 1, p.61-6, (1991) AbstractWebsite

Following the discovery of the tetraheme cytochrome c3 in the strict anaerobic sulfate-reducing bacteria (Postgate, J.R. (1954) Biochem. J. 59, xi; Ishimoto et al. (1954) Bull. Chem. Soc. Japan 27, 564-565), a variety of c-type cytochromes (and others) have been reported, indicating that the array of heme proteins in these bacteria is complex. We are proposing here a tentative classification of sulfate- (and sulfur-) reducing bacteria cytochromes c based on: number of hemes per monomer, heme axial ligation, heme spin state and primary structures (whole or fragmentary). Different and complementary spectroscopic tools have been used to reveal the structural features of the heme sites.

Redox studies on rubredoxins from sulphate and sulphur reducing bacteria, Moura, I., Moura J. J., Santos M. H., Xavier A. V., and Legall J. , FEBS Lett, Nov 15, Volume 107, Number 2, p.419-21, (1979) AbstractWebsite
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Isolation of P590 from Methanosarcina barkeri: evidence for the presence of sulfite reductase activity, Moura, J. J., Moura I., Santos H., Xavier A. V., Scandellari M., and Legall J. , Biochem Biophys Res Commun, Oct 15, Volume 108, Number 3, p.1002-9, (1982) AbstractWebsite
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Evidence for the formation of a cobalt-iron-sulfur (CoFe3S4) cluster in Desulfovibrio gigas ferredoxin II, Moura, Isabel, Moura Jose J. G., Munck Eckard, Papaefthymiou Vasilios, and Legall Jean , Journal of the American Chemical Society, 1986/01/01, Volume 108, Number 2, p.349-351, (1986) AbstractWebsite
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Mo and W bis-MGD enzymes: nitrate reductases and formate dehydrogenases, Moura, J. J., Brondino C. D., Trincao J., and Romao M. J. , J Biol Inorg Chem, Oct, Volume 9, Number 7, p.791-9, (2004) AbstractWebsite

Molybdenum and tungsten are second- and third-row transition elements, respectively, which are found in a mononuclear form in the active site of a diverse group of enzymes that generally catalyze oxygen atom transfer reactions. Mononuclear Mo-containing enzymes have been classified into three families: xanthine oxidase, DMSO reductase, and sulfite oxidase. The proteins of the DMSO reductase family present the widest diversity of properties among its members and our knowledge about this family was greatly broadened by the study of the enzymes nitrate reductase and formate dehydrogenase, obtained from different sources. We discuss in this review the information of the better characterized examples of these two types of Mo enzymes and W enzymes closely related to the members of the DMSO reductase family. We briefly summarize, also, the few cases reported so far for enzymes that can function either with Mo or W at their active site.

Flavodoxin and rubredoxin from Desulphovibrio salexigens, Moura, I., Moura J. J., Bruschi M., and Legall J. , Biochim Biophys Acta, Jun 10, Volume 591, Number 1, p.1-8, (1980) AbstractWebsite

A flavodoxin and a rubredoxin have been isolated from the sulfate-reducing bacterium Desulphovibrio salexigens (strain British Guiana, NICB 8403). Their amino acid composition and spectral characteristics did not differ markedly from the homologous proteins presented in other Desulphovibrio spp. Flavodoxin was shown to be active in the electron transport of the sulfite reductase system.