Export 1241 results:
Sort by: Author Title Type [ Year  (Desc)]
1998
Tavares, P, Pereira AS, Krebs C, Ravi N, Moura JJ, Moura I, Huynh BH.  1998.  Spectroscopic characterization of a novel tetranuclear Fe cluster in an iron-sulfur protein isolated from Desulfovibrio desulfuricans, Mar 3. Biochemistry. 37:2830-42., Number 9 AbstractWebsite

Mossbauer and EPR spectroscopies were used to characterize the Fe clusters in an Fe-S protein isolated from Desulfovibrio desulfuricans (ATCC 27774). This protein was previously thought to contain hexanuclear Fe clusters, but a recent X-ray crystallographic measurement on a similar protein isolated from Desulfovibrio vulgaris showed that the protein contains two tetranuclear clusters, a cubane-type [4Fe-4S] cluster and a mixed-ligand cluster of novel structure [Lindley et al. (1997) Abstract, Chemistry of Metals in Biological Systems, European Research Conference, Tomar, Portugal]. Three protein samples poised at different redox potentials (as-purified, 40 and 320 mV) were investigated. In all three samples, the [4Fe-4S] cluster was found to be present in the diamagnetic 2+ oxidation state and exhibited typical Mossbauer spectra. The novel-structure cluster was found to be redox active. In the 320-mV and as-purified samples, the cluster is at a redox equilibrium between its fully oxidized and one-electron reduced states. In the 40-mV sample, the cluster is in a two-electron reduced state. Distinct spectral components associated with the four Fe sites of cluster 2 in the three oxidation states were identified. The spectroscopic parameters obtained for the Fe sites reflect different ligand environments, making it possible to assign the spectral components to individual Fe sites. In the fully oxidized state, all four iron ions are high-spin ferric and antiferromagnetically coupled to form a diamagnetic S = 0 state. In the one-electron and two-electron reduced states, the reducing electrons were found to localize, consecutively, onto two Fe sites that are rich in oxygen/nitrogen ligands. Based on the X-ray structure and the Mossbauer parameters, attempts could be made to identify the reduced Fe sites. For the two-electron reduced cluster, EPR and Mossbauer data indicate that the cluster is paramagnetic with a nonzero interger spin. For the one-electron reduced cluster, the data suggest a half-integer spin of 9/2. Characteristic fine and hyperfine parameters for all four Fe sites were obtained. Structural implications and the nature of the spin-coupling interactions are discussed.

Kennedy, M, Yu L, Lima MJ, Ascenso CS, Czaja C, Moura I, Moura JJG, Rusnak F.  1998.  Metal binding to the tetrathiolate motif of desulforedoxin and related polypeptides, Dec. Journal of Biological Inorganic Chemistry. 3:643-649., Number 6 AbstractWebsite

Desulforedoxin and the N-terminus of desulfoferrodoxin share a 36 amino acid domain containing a (Cys-S)(4) metal binding site. Recombinant forms of desulforedoxin, an N-terminal fragment of desulfoferrodoxin, and two desulforedoxin mutant proteins were reconstituted with Fe3+ Cd2+, and Zn2+ and relative metal ion affinities assessed by proton titrations. Protons compete with metal for protein ligands, a process that can be followed by monitoring the optical spectrum of the metal-protein complex as a function of pH. For all polypeptides, Fe3+ bound with the highest affinity, whereas the affinity of Zn2+ was greater than Cd2+ in desulforedoxin and the N-terminal fragment of desulfoferrodoxin, but this order was reversed in desulforedoxin mutant proteins. Metal binding in both mutants was significantly impaired. Furthermore, the Fe3+ complex of both mutants underwent a time-dependent bleaching process which coincided with increased reactivity of cysteine residues to Ellman's reagent and concomitant metal dissociation. It is hypothesized that this results from an autoredox reaction in which Fe3+ is reduced to Fe2+ with attendant oxidation of ligand thiols.

Goodfellow, BJ, Rusnak F, Moura I, Domke T, Moura JJ.  1998.  NMR determination of the global structure of the 113Cd derivative of desulforedoxin: investigation of the hydrogen bonding pattern at the metal center, Apr. Protein Sci. 7:928-37., Number 4 AbstractWebsite

Desulforedoxin (Dx) is a simple homodimeric protein isolated from Desulfovibrio gigas (Dg) containing a distorted rubredoxin-like center with one iron coordinated by four cysteinyl residues (7.9 kDa with 36 amino acids per monomer). In order to probe the geometry and the H-bonding at the active site of Dx, the protein was reconstituted with 113Cd and the solution structure determined using 2D NMR methods. The structure of this derivative was initially compared with the NMR solution structure of the Zn form (Goodfellow BJ et al., 1996, J Biol Inorg Chem 1:341-353). Backbone amide protons for G4, D5, G13, L11 NH, and the Q14 NH side-chain protons, H-bonded in the X-ray structure, were readily exchanged with solvent. Chemical shift differences observed for amide protons near the metal center confirm the H-bonding pattern seen in the X-ray model (Archer M et al., 1995, J Mol Biol 251:690-702) and also suggest that H-bond lengths may vary between the Fe, Zn, and 113Cd forms. The H-bonding pattern was further probed using a heteronuclear spin echo difference (HSED) experiment; the results confirm the presence of NH-S H-bonds inferred from D2O exchange data and observed in the NMR family of structures. The presence of "H-bond mediated" coupling in Dx indicates that the NH-S H-bonds at the metal center have significant covalent character. The HSED experiment also identified an intermonomer "through space" coupling for one of the L26 methyl groups, indicating its proximity to the 113Cd center in the opposing monomer. This is the first example of an intermonomer "through space" coupling. Initial structure calculations produced subsets of NMR families with the S of C28 pointing away from or toward the L26 methyl: only the subset with the C28 sulfur pointing toward the L26 methyl could result in a "through space" coupling. The HSED result was therefore included in the structure calculations. Comparison of the Fe, Zn, and 113Cd forms of Dx suggests that the geometry of the metal center and the global fold of the protein does not vary to any great extent, although the H-bond network varies slightly when Cd is introduced. The similarity between the H-bonding pattern seen at the metal center in Dx, Rd (including H-bonded and through space-mediated coupling), and many zinc-finger proteins suggests that these H-bonds are structurally vital for stabilization of the metal centers in these proteins.

Goncalves, IS, Kuhn FE, Lopes AD, Parola AJ, Pina F, Sotomayor J, Romao CC.  1998.  Synthesis and characterization of binuclear transition metal rhenium(VII) complexes with bridging cyanide ligands, 1998. Journal of Organometallic Chemistry. 560:117-124. AbstractWebsite

Reacting transition metal complexes in low oxidation states, containing one or two cyanide ligands, with methyltrioxorhenium(VII) leads to bridged mixed metal compounds in good yields. The Re(VII) core is then surrounded by five or six ligands, respectively. The strength of these CN bridges and thus the stability of the newly generated bimetallic compound strongly depends on the donor strength of the ligands surrounding of the Cr/Mo/W or Fe moiety. The stability of the mixed metal molecules is reflected in the temperature dependent behavior of their O-17-NMR spectra, in their IR (Re=O) stretching frequencies and force constants, as well as several other spectroscopic data. UV-vis absorption spectra show the appearance of charge transfer bands. In the case of the mixed Mo/Re complexes the Mo-95-NMR spectroscopy is also a helpful tool to examine the donor capability of the Mo moiety. The described compounds also show photosensitivity. (C) 1998 Elsevier Science S.A. All rights reserved.

Glatigny, A, Hof P, Romao MJ, Huber R, Scazzocchio C.  1998.  Altered specificity mutations define residues essential for substrate positioning in xanthine dehydrogenase. Journal of Molecular Biology. 278:431-438., Number 2 AbstractWebsite
n/a
Pina, F, Roque A.  1998.  Ion-pairing co-pigmentation with 4 ',7-dihydroxyflavylium studied by pulse light jumps. Journal of Photochemistry and Photobiology a-Chemistry. 114:59-64., Number 1 AbstractWebsite
n/a
Pina, F, Roque A, Melo MJ, Maestri I, Belladelli L, Balzani V.  1998.  Multislate/multifunctional molecular-level systems: Light and pH switching between the various forms of a synthetic flavylium salt. Chemistry-a European Journal. 4:1184-1191., Number 7 AbstractWebsite
n/a
Vigil, MR, Renamayor CS, Pierola I, Lima JC, Melo EC, Macanita AL.  1998.  Non-diffusion-controlled excimer formation with indane and acenaphthene. Kinetics and thermodynamics from picosecond-time-resolved fluorescence. Chemical Physics Letters. 287:379-387., Number 3-4 Abstract
n/a
Tavares, P, Pereira AS, Krebs C, Ravi N, Moura JJG, Moura I, Huynh BH.  1998.  Spectroscopic characterization of a novel tetranuclear Fe cluster in an iron-sulfur protein isolated from Desulfovibrio desulfuricans. Biochemistry. {37}:{2830-2842}., Number {9} Abstract

Mossbauer and EPR spectroscopies were used to characterize the Fe clusters in an Fe-S protein isolated from Desulfovibrio desulfuricans (ATCC 27774). This protein was previously thought to contain hexanuclear Fe clusters, but a recent X-ray crystallographic measurement on a similar protein isolated from Desulfovibrio vulgaris showed that the protein contains two tetranuclear clusters, a cubane-type [4Fe-4S] cluster and a mixed-ligand cluster of novel structure [Lindley et al. (1997) Abstract, Chemistry of Metals in Biological Systems, European Research Conference, Tomar, Portugal]. Three protein samples poised at different redox potentials (as-purified, 40 and 320 mV) were investigated. In all three samples, the [4Fe-4S] cluster was found to be present in the diamagnetic 2+ oxidation state and exhibited typical Mossbauer spectra. The novel-structure cluster was found to be redox active. In the 320-mV and as-purified samples, the cluster is at a redox equilibrium between its fully oxidized and one-electron reduced states. In the 40-mV sample, the cluster is in a two-electron reduced state. Distinct spectral components associated with the four Fe sites of cluster 2 in the three oxidation states were identified. The spectroscopic parameters obtained for the Fe sites reflect different ligand environments, making it possible to assign the spectral components to individual Fe sites. In the fully oxidized state, all four iron ions are high-spin ferric and antiferromagnetically coupled to form a diamagnetic S = 0 state. In the one-electron and two-electron reduced states, the reducing electrons were found to localize, consecutively, onto two Fe sites that are rich in oxygen/nitrogen ligands. Based on the X-ray structure and the Mossbauer parameters, attempts could be made to identify the reduced Fe sites. For the two-electron reduced cluster, EPR and Mossbauer data indicate that the cluster is paramagnetic with a nonzero interger spin. For the one-electron reduced cluster, the data suggest a half-integer spin of 9/2 Characteristic fine and hyperfine parameters for all four Fe sites were obtained. Structural implications and the nature of the spin-coupling interactions are discussed.

Romao, MJ, Huber R.  1998.  Structure and function of the xanthine-oxidase family of molybdenum enzymes. Metal Sites in Proteins and Models. 90:69-95. AbstractWebsite
n/a
Voityuk, AA, Albert K, Romao MJ, Huber R, Rosch N.  1998.  Substrate oxidation in the active site of xanthine oxidase and related enzymes. A model density functional study. Inorganic Chemistry. 37:176-180., Number 2 AbstractWebsite
n/a
Bernardo, MA, Pina F, Garcia-Espana E, Latorre J, Luis SV, Llinares JM, Ramirez JA, Soriano C.  1998.  Thermodynamic and steady-state fluorescence emission studies on metal complexes of receptors containing benzene subunits. Inorganic Chemistry. 37:3935-3942., Number 16 AbstractWebsite
n/a
1997
Rosa, AM, Lobo AM, Branco PS, Prabhakar S, SadaCosta M.  1997.  New syntheses of the Amaryllidacaea alkaloids vasconine, assoanine, oxoassoanine, pratosine and ismine by radical cyclisation, JAN 6. TETRAHEDRON. 53:299-306., Number 1 Abstract
n/a
Rosa, AM, Lobo AM, Branco PS, Prabhakar S, Pereira AMDL.  1997.  Synthesis of phenanthridines by radical C-aryl-C-aryl coupling, JAN 6. TETRAHEDRON. 53:269-284., Number 1 Abstract
n/a
Duarte, RO, Reis AR, Girio F, Moura I, Moura JJ, Collaco TA.  1997.  The formate dehydrogenase isolated from the aerobe Methylobacterium sp. RXM is a molybdenum-containing protein, Jan 3. Biochem Biophys Res Commun. 230:30-4., Number 1 AbstractWebsite

The formate dehydrogenase (FDH) isolated from cells of Methylobacterium sp. RXM grown on molybdenum-containing mineral medium using methanol as carbon source, was partially purified (at least 90% pure as revealed by SDS-PAGE). The enzyme is unstable under oxygen and all the purification steps were conducted under strict anaerobic conditions. The molecular mass is 75 kDa (gel exclusion 300 kDa). The enzyme was characterized in terms of the kinetic parameters towards different substrates and electron acceptors, pH and temperature dependence and the effect of a wide range of compounds in the enzymatic activity. The EPR spectra of the dithionite reduced sample show, at low temperature (below 20 K), two rhombic EPR signals due to two distinct [Fe-S] centres (centre I at g-values 2.023, 1.951 and 1.933, and centre II at g-values 2.054 and 1.913). At high temperature (around 100 K) another rhombic EPR signal is optimally observed at g-values 2.002, 1.987 and 1.959 and attributed to the molybdenum site. The EPR signals assigned to the iron-sulfur centres show a strong analogy with the aldehyde oxido-reductase from Desulfovibrio gigas known to contain a Mo-pterin and two [2Fe-2S] centres and whose crystallographic structure was recently resolved.

Yu, L, Kennedy M, Czaja C, Tavares P, Moura JJ, Moura I, Rusnak F.  1997.  Conversion of desulforedoxin into a rubredoxin center, Feb 24. Biochem Biophys Res Commun. 231:679-82., Number 3 AbstractWebsite

Rubredoxin and desulforedoxin both contain an Fe(S-Cys)4 center. However, the spectroscopic properties of the center in desulforedoxin differ from rubredoxin. These differences arise from a distortion of the metal site hypothesized to result from adjacent cysteine residues in the primary sequence of desulforedoxin. Two desulforedoxin mutants were generated in which either a G or P-V were inserted between adjacent cysteines. Both mutants exhibited optical spectra with maxima at 278, 345, 380, 480, and 560 nm while the low temperature X-band EPR spectra indicated highspin Fe3+ ions with large rhombic distortions (E/D = 0.21-0.23). These spectroscopic properties are distinct from wild type desulforedoxin and virtually identical to rubredoxin.

Franco, R, Calvete JJ, Thole HH, Raida M, Moura I, Moura JJG.  1997.  The primary structure of the beta subunit of Desulfovibrio desulfuricans (ATCC 27774) NiFe hydrogenase, Apr. Protein and Peptide Letters. 4:131-138., Number 2 AbstractWebsite

The periplasmic [NiFe] hydrogenase isolated from Desulfovibrio (D.) desulfuricans (ATCC 27774) is a heterodimer of a 28 kDa (beta) and a 60 kDa (alpha) subunit. Here we report the complete amino acid sequence of the small (beta) polypeptide chain determined by Edman degradation of proteolytic fragments. Electrospray-ionization mass spectrometry of the native protein confirmed the sequencing results. The sequence is compared with that of D. gigas [NiFe] hydrogenase whose three-dimensional structure has been recently published.

Silva, RN, Rato LM, Lemos JM, Coito F.  1997.  Cascade control of a distributed collector solar field. Journal of Process Control. 7:111–117(Number 2):Elsevier. Abstract

n/a

Varela, PF, Romero A, Sanz L, Romao MJ, Topfer-Petersen E, Calvete JJ.  1997.  The 2.4 angstrom resolution crystal structure of boar seminal plasma PSP-I/PSP-II: a zona pellucida-binding glycoprotein heterodimer of the spermadhesin family built by a CUB domain architecture. Journal of Molecular Biology. 274:635-649., Number 4 AbstractWebsite
n/a
Silva, RN, Rato LM, Lemos JM, Coito F.  1997.  Cascade control of a distributed collector solar field. Journal of Process Control. 7:111–117., Number 2: Elsevier Abstract

n/a

Yu, L, Kennedy M, Czaja C, Tavares P, Moura JJG, Moura I, Rusnak F.  1997.  Conversion of desulforedoxin into a rubredoxin center. Biochemical And Biophysical Research Communications. {231}:{679-682}., Number {3} Abstract

Rubredoxin and desulforedoxin both contain an Fe(S-Cys)(4) center, However the spectroscopic properties of the center in desulforedoxin differ from rubredoxin, These differences arise from a distortion of the metal site hypothesized to result from adjacent cysteine residues in the primary sequence of desulforedoxin. Two desulforedoxin mutants were generated in which either a G or P-V were inserted between adjacent cysteines. Both mutants exhibited optical spectra with maxima at 278, 345, 380, 480, and 560 nm while the low temperature X-band EPR spectra indicated high-spin Fe3+ ions with large rhombic distortions (E/D = 0.21-0.23). These spectroscopic properties are distinct from wild type desulforedoxin and virtually identical to rubredoxin. (C) 1997 Academic Press.

Romao, MJ, Hubert R.  1997.  Crystal structure and mechanism of action of the xanthine oxidase-related aldehyde oxidoreductase from Desulfovibrio gigas. Biochemical Society Transactions. 25:755-757., Number 3 AbstractWebsite
n/a
Romao, MJ, Kolln I, Dias JM, Carvalho AL, Romero A, Varela PF, Sanz L, Topfer-Petersen E, Calvete JJ.  1997.  Crystal structure of acidic seminal fluid protein (aSFP) at 1.9 angstrom resolution: a bovine polypeptide of the spermadhesin family. Journal of Molecular Biology. 274:650-660., Number 4 AbstractWebsite
n/a
Archer, M, Banci L, Dikaya E, Romao MJ.  1997.  Crystal structure of cytochrome c' from Rhodocyclus gelatinosus and comparison with other cytochromes c'. Journal of Biological Inorganic Chemistry. 2:611-622., Number 5 AbstractWebsite
n/a
loading