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2006
Meil, P, Trommel W, Bannink D, Hoogenboom M, Moniz A, Woll T, Makó C, Csizmadia P, Illessy M, Balkmar D, Linardos P.  2006.  Comparative report - WORKS WP5 Policy pillar, May. , Number 67056: ZBW - German National Library of Economics Abstract

This report begins with some general information and analysis of policy and regulation that were the subjects of discussion and exchange in the policy pillar in the first phase of WORKS. The second section is a synthesis of country information on general principles and trends of policy and policy enforcement. This is followed by a summary of sector information for the sectors chosen by the qualitative pillar to be the objects of empirical analysis. The last summarises research questions and dimensions to be guidelines for carrying out case studies and capturing the relevance and effects of policy and institutions at the workplace. –

Meil, P, Trommel W, Bannink D, Hoogenboom M, Moniz A, Woll T, Makó C, Csizmadia P, Illessy M, Balkmar D, Linardos P.  2006.  {Comparative report - WORKS WP5 Policy pillar}, May. , Number 67056: ZBW - German National Library of Economics Abstract

This report begins with some general information and analysis of policy and regulation that were the subjects of discussion and exchange in the policy pillar in the first phase of WORKS. The second section is a synthesis of country information on general principles and trends of policy and policy enforcement. This is followed by a summary of sector information for the sectors chosen by the qualitative pillar to be the objects of empirical analysis. The last summarises research questions and dimensions to be guidelines for carrying out case studies and capturing the relevance and effects of policy and institutions at the workplace.

Meil, P, Trommel W, Bannink D, Hoogenboom M, Moniz A, Woll T, Makó C, Csizmadia P, Illessy M, Balkmar D, Linardos P.  2006.  {Comparative report - WORKS WP5 Policy pillar}. , Number 67056: ZBW - German National Library of Economics Abstract

This report begins with some general information and analysis of policy and regulation that were the subjects of discussion and exchange in the policy pillar in the first phase of WORKS. The second section is a synthesis of country information on general principles and trends of policy and policy enforcement. This is followed by a summary of sector information for the sectors chosen by the qualitative pillar to be the objects of empirical analysis. The last summarises research questions and dimensions to be guidelines for carrying out case studies and capturing the relevance and effects of policy and institutions at the workplace.

2005
Baptista, {PMRV}, c}alo Dória G{\c, Henriques D, Pereira E, Franco R.  2005.  Colorimetric detection of eukaryotic gene expression with DNA-derivatized gold nanoparticles, jan. Journal of Biotechnology. 119:111–7., Number 2: Elsevier Abstract

Thiol-linked DNA-gold nanoparticles were used in a novel colorimetric method to detect the presence of specific mRNA from a total RNA extract of yeast cells. The method allowed detection of expression of the FSY1 gene that encodes a specific fructose/H+ symporter in Saccharomyces bayanus PYCC 4565. FSY1 is strongly expressed when the yeast is grown in fructose as the sole carbon source, while cells cultivated in glucose as the sole carbon source repress gene expression. The presence of FSY1 mRNA is detected based on color change of a sample containing total RNA extracted from the organism and gold nanoparticles derivatized with a 15-mer of complementary single stranded DNA upon addition of NaCl. If FSY1 mRNA is present, the solution remains pink, changing to blue-purple in the absence of FSY1 mRNA. Direct detection of specific expression was possible from only 0.3 microg of unamplified total RNA without any further enhancement. This novel method is inexpensive, very easy to perform as no amplification or signal enhancement steps are necessary and takes less than 15 min to develop after total RNA extraction. No temperature control is necessary and color change can be easily detected visually.

Simões, S, Seixas J, Huppes G.  2005.   tangled web: assessing overlaps between energy and environmental policy instruments in place along electricity systems, 30 May - 3 June. ECEEE - European Council for an Energy Efficient Economy 2005 Summer Study. , Mandelieu, France
2004
Pauleta, SR, Cooper A, Nutley M, Errington N, Harding S, Guerlesquin F, Goodhew CF, Moura I, Moura JJ, Pettigrew GW.  2004.  A copper protein and a cytochrome bind at the same site on bacterial cytochrome c peroxidase, Nov 23. Biochemistry. 43:14566-76., Number 46 AbstractWebsite

Pseudoazurin binds at a single site on cytochrome c peroxidase from Paracoccus pantotrophus with a K(d) of 16.4 microM at 25 degrees C, pH 6.0, in an endothermic reaction that is driven by a large entropy change. Sedimentation velocity experiments confirmed the presence of a single site, although results at higher pseudoazurin concentrations are complicated by the dimerization of the protein. Microcalorimetry, ultracentrifugation, and (1)H NMR spectroscopy studies in which cytochrome c550, pseudoazurin, and cytochrome c peroxidase were all present could be modeled using a competitive binding algorithm. Molecular docking simulation of the binding of pseudoazurin to the peroxidase in combination with the chemical shift perturbation pattern for pseudoazurin in the presence of the peroxidase revealed a group of solutions that were situated close to the electron-transferring heme with Cu-Fe distances of about 14 A. This is consistent with the results of (1)H NMR spectroscopy, which showed that pseudoazurin binds closely enough to the electron-transferring heme of the peroxidase to perturb its set of heme methyl resonances. We conclude that cytochrome c550 and pseudoazurin bind at the same site on the cytochrome c peroxidase and that the pair of electrons required to restore the enzyme to its active state after turnover are delivered one-by-one to the electron-transferring heme.

Dey, A, Glaser T, Moura JJ, Holm RH, Hedman B, Hodgson KO, Solomon EI.  2004.  Ligand K-edge X-ray absorption spectroscopy and DFT calculations on [Fe3S4]0,+ clusters: delocalization, redox, and effect of the protein environment, Dec 29. J Am Chem Soc. 126:16868-78., Number 51 AbstractWebsite

Ligand K-edge XAS of an [Fe3S4]0 model complex is reported. The pre-edge can be resolved into contributions from the mu(2)S(sulfide), mu(3)S(sulfide), and S(thiolate) ligands. The average ligand-metal bond covalencies obtained from these pre-edges are further distributed between Fe(3+) and Fe(2.5+) components using DFT calculations. The bridging ligand covalency in the [Fe2S2]+ subsite of the [Fe3S4]0 cluster is found to be significantly lower than its value in a reduced [Fe2S2] cluster (38% vs 61%, respectively). This lowered bridging ligand covalency reduces the superexchange coupling parameter J relative to its value in a reduced [Fe2S2]+ site (-146 cm(-1) vs -360 cm(-1), respectively). This decrease in J, along with estimates of the double exchange parameter B and vibronic coupling parameter lambda2/k(-), leads to an S = 2 delocalized ground state in the [Fe3S4]0 cluster. The S K-edge XAS of the protein ferredoxin II (Fd II) from the D. gigas active site shows a decrease in covalency compared to the model complex, in the same oxidation state, which correlates with the number of H-bonding interactions to specific sulfur ligands present in the active site. The changes in ligand-metal bond covalencies upon redox compared with DFT calculations indicate that the redox reaction involves a two-electron change (one-electron ionization plus a spin change of a second electron) with significant electronic relaxation. The presence of the redox inactive Fe(3+) center is found to decrease the barrier of the redox process in the [Fe3S4] cluster due to its strong antiferromagnetic coupling with the redox active Fe2S2 subsite.

Hettmann, T, Siddiqui RA, Frey C, Santos-Silva T, Romao MJ, Diekmann S.  2004.  Mutagenesis study on amino acids around the molybdenum centre of the periplasmic nitrate reductase from Ralstonia eutropha. Biochemical and Biophysical Research Communications. 320:1211-1219., Number 4 AbstractWebsite
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Helberger, N, Kerényi K, Krings B, Lambers R, Orwat C, Riehm U, van Gompel S, Dufft N.  2004.  {Digital Rights Management and Consumer Acceptability: A Multi-Disciplinary Discussion of Consumer Concerns and Expectations}. , Number 6641: University Library of Munich, Germany Abstract

The INDICARE project – the Informed Dialogue about Consumer Acceptability of DRM Solutions in Europe – has been set up to raise awareness about consumer and user issues of Digital Rights Management (DRM) solutions. One of the main goals of the INDICARE project is to contribute to the consensus-building among multiple players with heterogeneous interests in the digital environment. To promote this process and to contribute to the creation of a common level of understanding is the aim of the present report. It provides an overview of consumer concerns and expectations regarding DRMs, and discusses the findings from a social, legal, technical and business perspective. A general overview of the existing EC initiatives shows that questions of consumer acceptability of DRM have only recently begun to draw wider attention. A review of the relevant statements, studies and reports confirms that awareness of consumer concerns is still at a low level. Five major categories of concerns have been distinguished so far: (1) fair conditions of use and access to digital content, (2) privacy, (3) interoperability, (4) transparency and (5) various aspects of consumer friendliness. From the legal point of view, many of the identified issues go beyond the scope of copyright law, i.e. the field of law where DRM was traditionally discussed. Often they are a matter of general or sector-specific consumer protection law. Furthermore, it is still unclear to what extent technology and an appropriate design of technical solutions can provide an answer to some of the concerns of consumers. One goal of the technical chapter was exactly to highlight some of these technical possibilities. Finally, it is shown that consumer acceptability of DRM is important for the economic success of different business models based on DRM. Fair and responsive DRM design can be a profitable strategy, however DRM-free alternatives do exist too.

2003
Andersen, NH, Harnung SE, Trabjerg I, Moura I, Moura JJG, Ulstrup J.  2003.  Broad-temperature range spectroscopy of the two-centre modular redox metalloprotein Desulfovibrio desulfuricans desulfoferrodoxin, Sep 7. Dalton Transactions. :3328-3338., Number 17 AbstractWebsite

The electronic-vibrational couplings of the two-centre non-heme iron protein Desulfovibrio desulfuricans desulfoferrodoxin (DFx) in three oxidation states, i.e. fully oxidised (grey), half-oxidised (pink), and fully reduced (colourless), have been investigated by variable temperature (VT) UV/VIS, MCD, CD, and EPR spectroscopy. The UV/VIS spectra of grey DFx at room temperature is characterised by broad charge transfer (CT) transitions associated with oxidised centre 1 (495 and 368 nm) and II (335 and 635 nm). The transitions are resolved at 78 K, substantiated by VT-MCD and -CD. The data offer novel information about the electronic-vibrational couplings of the transitions. Multiphonon bandshape analysis discloses strong contributions from both local Fe-S and S-C stretching and solvent/protein modes. A number of transitions are blue- or red-shifted compared with monomeric desulforedoxin, superoxide reductase or dismutase, and cloned Desulfovibrio vulgaris DFx fragments. Conversion from grey to pink DFx is accompanied by drastic electronic-vibrational changes of both centres. The data suggest that electron transfer and optical CT-transitions of DFx are controlled by environmental reorganization in the whole region between the metal centres.

Pettigrew, GW, Pauleta SR, Goodhew CF, Cooper A, Nutley M, Jumel K, Harding SE, Costa C, Krippahl L, Moura I, Moura J.  2003.  Electron transfer complexes of cytochrome c peroxidase from Paracoccus denitrificans containing more than one cytochrome, Oct 21. Biochemistry. 42:11968-81., Number 41 AbstractWebsite

According to the model proposed in previous papers [Pettigrew, G. W., Prazeres, S., Costa, C., Palma, N., Krippahl, L., and Moura, J. J. (1999) The structure of an electron-transfer complex containing a cytochrome c and a peroxidase, J. Biol. Chem. 274, 11383-11389; Pettigrew, G. W., Goodhew, C. F., Cooper, A., Nutley, M., Jumel, K., and Harding, S. E. (2003) Electron transfer complexes of cytochrome c peroxidase from Paracoccus denitrificans, Biochemistry 42, 2046-2055], cytochrome c peroxidase of Paracoccus denitrificans can accommodate horse cytochrome c and Paracoccus cytochrome c(550) at different sites on its molecular surface. Here we use (1)H NMR spectroscopy, analytical ultracentrifugation, molecular docking simulation, and microcalorimetry to investigate whether these small cytochromes can be accommodated simultaneously in the formation of a ternary complex. The pattern of perturbation of heme methyl and methionine methyl resonances in binary and ternary solutions shows that a ternary complex can be formed, and this is confirmed by the increase in the sedimentation coefficient upon addition of horse cytochrome c to a solution in which cytochrome c(550) fully occupies its binding site on cytochrome c peroxidase. Docking experiments in which favored binary solutions of cytochrome c(550) bound to cytochrome c peroxidase act as targets for horse cytochrome c and the reciprocal experiments in which favored binary solutions of horse cytochrome c bound to cytochrome c peroxidase act as targets for cytochrome c(550) show that the enzyme can accommodate both cytochromes at the same time on adjacent sites. Microcalorimetric titrations are difficult to interpret but are consistent with a weakened binding of horse cytochrome c to a binary complex of cytochrome c peroxidase and cytochrome c(550) and binding of cytochrome c(550) to the cytochrome c peroxidase that is affected little by the presence of horse cytochrome c in the other site. The presence of a substantial capture surface for small cytochromes on the cytochrome c peroxidase has implications for rate enhancement mechanisms which ensure that the two electrons required for re-reduction of the enzyme after reaction with hydrogen peroxide are delivered efficiently.

Almeida, MG, Macieira S, Goncalves LL, Huber R, Cunha CA, Romao MJ, Costa C, Lampreia J, Moura JJ, Moura I.  2003.  The isolation and characterization of cytochrome c nitrite reductase subunits (NrfA and NrfH) from Desulfovibrio desulfuricans ATCC 27774. Re-evaluation of the spectroscopic data and redox properties, Oct. Eur J Biochem. 270:3904-15., Number 19 AbstractWebsite

The cytochrome c nitrite reductase is isolated from the membranes of the sulfate-reducing bacterium Desulfovibrio desulfuricans ATCC 27774 as a heterooligomeric complex composed by two subunits (61 kDa and 19 kDa) containing c-type hemes, encoded by the genes nrfA and nrfH, respectively. The extracted complex has in average a 2NrfA:1NrfH composition. The separation of ccNiR subunits from one another is accomplished by gel filtration chromatography in the presence of SDS. The amino-acid sequence and biochemical subunits characterization show that NrfA contains five hemes and NrfH four hemes. These considerations enabled the revision of a vast amount of existing spectroscopic data on the NrfHA complex that was not originally well interpreted due to the lack of knowledge on the heme content and the oligomeric enzyme status. Based on EPR and Mossbauer parameters and their correlation to structural information recently obtained from X-ray crystallography on the NrfA structure [Cunha, C.A., Macieira, S., Dias, J.M., Almeida, M.G., Goncalves, L.M.L., Costa, C., Lampreia, J., Huber, R., Moura, J.J.G., Moura, I. & Romao, M. (2003) J. Biol. Chem. 278, 17455-17465], we propose the full assignment of midpoint reduction potentials values to the individual hemes. NrfA contains the high-spin catalytic site (-80 mV) as well as a quite unusual high reduction potential (+150 mV)/low-spin bis-His coordinated heme, considered to be the site where electrons enter. In addition, the reassessment of the spectroscopic data allowed the first partial spectroscopic characterization of the NrfH subunit. The four NrfH hemes are all in a low-spin state (S = 1/2). One of them has a gmax at 3.55, characteristic of bis-histidinyl iron ligands in a noncoplanar arrangement, and has a positive reduction potential.

Cunha, CA, Macieira S, Dias JM, Almeida G, Goncalves LL, Costa C, Lampreia J, Huber R, Moura JJ, Moura I, Romao MJ.  2003.  Cytochrome c nitrite reductase from Desulfovibrio desulfuricans ATCC 27774. The relevance of the two calcium sites in the structure of the catalytic subunit (NrfA), May 9. J Biol Chem. 278:17455-65., Number 19 AbstractWebsite

The gene encoding cytochrome c nitrite reductase (NrfA) from Desulfovibrio desulfuricans ATCC 27774 was sequenced and the crystal structure of the enzyme was determined to 2.3-A resolution. In comparison with homologous structures, it presents structural differences mainly located at the regions surrounding the putative substrate inlet and product outlet, and includes a well defined second calcium site with octahedral geometry, coordinated to propionates of hemes 3 and 4, and caged by a loop non-existent in the previous structures. The highly negative electrostatic potential in the environment around hemes 3 and 4 suggests that the main role of this calcium ion may not be electrostatic but structural, namely in the stabilization of the conformation of the additional loop that cages it and influences the solvent accessibility of heme 4. The NrfA active site is similar to that of peroxidases with a nearby calcium site at the heme distal side nearly in the same location as occurs in the class II and class III peroxidases. This fact suggests that the calcium ion at the distal side of the active site in the NrfA enzymes may have a similar physiological role to that reported for the peroxidases.

Timoteo, CG, Tavares P, Goodhew CF, Duarte LC, Jumel K, Girio FMF, Harding S, Pettigrew GW, Moura I.  2003.  Ca2+ and the bacterial peroxidases: the cytochrome c peroxidase from Pseudomonas stutzeri, Jan. Journal of Biological Inorganic Chemistry. 8:29-37., Number 1-2 AbstractWebsite

The production of cytochrome c peroxidase (CCP) from Pseudomonas (Ps.) stutzeri (ATCC 11607) was optimized by adjusting the composition of the growth medium and aeration of the culture. The protein was isolated and characterized biochemically and spectroscopically in the oxidized and mixed valence forms. The activity of Ps. stutzeri CCP was studied using two different ferrocytochromes as electron donors: Ps. stutzeri cytochrome C-551 (the physiological electron donor) and horse heart cytochrome c. These electron donors interact differently with Ps. stutzeri CCP, exhibiting different ionic strength dependence. The CCP from Paracoccus (Pa.) denitrificans was proposed to have two different Ca2+ binding sites: one usually occupied (site I) and the other either empty or partially occupied in the oxidized enzyme (site II). The Ps. stutzeri enzyme was purified in a form with tightly bound Ca2+. The affinity for Ca2+ in the mixed valence enzyme is so high that Ca2+ returns to it from the EGTA which was added to empty the site in the oxidized enzyme. Molecular mass determination by ultracentrifugation and behavior on gel filtration chromatography have revealed that this CCP is isolated as an active dimer, in contrast to the Pa. denitrificans CCP which requires added Ca2+ for formation of the dimer and also for activation of the enzyme. This is consistent with the proposal that Ca2+ in the bacterial peroxidases influences the monomer/dimer equilibrium and the transition to the active form of the enzyme. Additional Ca2+ does affect both the kinetics of oxidation of horse heart cytochrome c (but not cytochrome C-551) and higher aggregation states of the enzyme. This suggests the presence of a superficial Ca2+ binding site of low affinity.

Timóteo, CG, Tavares P, Goodhew CF, Duarte LC, Jumel K, Girio FMF, Harding S, Pettigrew GW, Moura I.  2003.  Ca2+ and the bacterial peroxidases: the cytochrome c peroxidase from Pseudomonas stutzeri, Feb. JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY. {8}:{29-37}., Number {1-2} Abstract

The production of cytochrome c peroxidase (CCP) from Pseudomonas (Ps.) stutzeri (ATCC 11607) was optimized by adjusting the composition of the growth medium and aeration of the culture. The protein was isolated and characterized biochemically and spectroscopically in the oxidized and mixed valence forms. The activity of Ps. stutzeri CCP was studied using two different ferrocytochromes as electron donors: Ps. stutzeri cytochrome C-551 (the physiological electron donor) and horse heart cytochrome c. These electron donors interact differently with Ps. stutzeri CCP, exhibiting different ionic strength dependence. The CCP from Paracoccus (Pa.) denitrificans was proposed to have two different Ca2+ binding sites: one usually occupied (site I) and the other either empty or partially occupied in the oxidized enzyme (site II). The Ps. stutzeri enzyme was purified in a form with tightly bound Ca2+. The affinity for Ca2+ in the mixed valence enzyme is so high that Ca2+ returns to it from the EGTA which was added to empty the site in the oxidized enzyme. Molecular mass determination by ultracentrifugation and behavior on gel filtration chromatography have revealed that this CCP is isolated as an active dimer, in contrast to the Pa. denitrificans CCP which requires added Ca2+ for formation of the dimer and also for activation of the enzyme. This is consistent with the proposal that Ca2+ in the bacterial peroxidases influences the monomer/dimer equilibrium and the transition to the active form of the enzyme. Additional Ca2+ does affect both the kinetics of oxidation of horse heart cytochrome c (but not cytochrome C-551) and higher aggregation states of the enzyme. This suggests the presence of a superficial Ca2+ binding site of low affinity.

Huynh, BH, Tavares P, Pereira AS, Moura I, Moura JJG.  2003.  Reductive activation of aerobically purified Desulfovibrio vulgaris hydrogenase: Mossbauer characterization of the catalytic H cluster, 2003. Biochemistry and Physiology of Anaerobic Bacteria. :35-45. AbstractWebsite
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Bandeiras, TM, Salgueiro CA, Huber H, Gomes CM, Teixeira M.  2003.  The respiratory chain of the thermophilic archaeon Sulfolobus metallicus: studies on the type-II NADH dehydrogenase. Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1557(1-3):13-19. AbstractWebsite

The membranes of the thermoacidophilic archaeon Sulfolobus metallicus exhibit an oxygen consumption activity of 0.5 nmol O2 min−1 mg−1, which is insensitive to rotenone, suggesting the presence of a type-II NADH dehydrogenase. Following this observation, the enzyme was purified from solubilised membranes and characterised. The pure protein is a monomer with an apparent molecular mass of 49 kDa, having a high N-terminal amino acid sequence similarity towards other prokaryotic enzymes of the same type. It contains a covalently attached flavin, which was identified as being FMN by 31P-NMR spectroscopy, a novelty among type-II NADH dehydrogenases. Metal analysis showed the absence of iron, indicating that no FeS clusters are present in the protein. The average reduction potential of the FMN group was determined to be +160 mV, at 25 °C and pH 6.5, by redox titrations monitored by visible spectroscopy. Catalytically, the enzyme is a NADH:quinone oxidoreductase, as it is capable of transferring electrons from NADH to several quinones, including ubiquinone-1, ubiquinone-2 and caldariella quinone. Maximal turnover rates of 195 μmol NADH oxidized min−1 mg−1 at 60 °C were obtained using ubiquinone-2 as electron acceptor, after enzyme dilution and incubation with phospholipids.

Cunha, CA, Macieira S, Dias JM, Almeida G, Goncalves LL, Costa C, Lampreia J, Huber R, Moura JJG, Moura I, Romao MJ.  2003.  Cytochrome c nitrite reductase from Desulfovibrio desulfuricans ATCC 27774 - The relevance of the two calcium sites in the structure of the catalytic subunit (NrfA). Journal of Biological Chemistry. 278:17455-17465., Number 19 AbstractWebsite
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Almeida, MG, Macieira S, Goncalves LL, Huber R, Cunha CA, Romao MJ, Costa C, Lampreia J, Moura JJG, Moura I.  2003.  The isolation and characterization of cytochrome c nitrite reductase subunits (NrfA and NrfH) from Desulfovibrio desulfuricans ATCC 27774 - Re-evaluation of the spectroscopic data and redox properties. European Journal of Biochemistry. 270:3904-3915., Number 19 AbstractWebsite
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Hettmann, T, Siddiqui RA, van Langen J, Frey C, Romao MJ, Diekmann S.  2003.  Mutagenesis study on the role of a lysine residue highly conserved in formate dehydrogenases and periplasmic nitrate reductases. Biochemical and Biophysical Research Communications. 310:40-47., Number 1 AbstractWebsite
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2002
Raaijmakers, H, Macieira S, Dias JM, Teixeira S, Bursakov S, Huber R, Moura JJ, Moura I, Romao MJ.  2002.  Gene sequence and the 1.8 A crystal structure of the tungsten-containing formate dehydrogenase from Desulfovibrio gigas, Sep. Structure. 10:1261-72., Number 9 AbstractWebsite

Desulfovibrio gigas formate dehydrogenase is the first representative of a tungsten-containing enzyme from a mesophile that has been structurally characterized. It is a heterodimer of 110 and 24 kDa subunits. The large subunit, homologous to E. coli FDH-H and to D. desulfuricans nitrate reductase, harbors the W site and one [4Fe-4S] center. No small subunit ortholog containing three [4Fe-4S] clusters has been reported. The structural homology with E. coli FDH-H shows that the essential residues (SeCys158, His159, and Arg407) at the active site are conserved. The active site is accessible via a positively charged tunnel, while product release may be facilitated, for H(+) by buried waters and protonable amino acids and for CO(2) through a hydrophobic channel.

Carepo, M, Tierney DL, Brondino CD, Yang TC, Pamplona A, Telser J, Moura I, Moura JJ, Hoffman BM.  2002.  17O ENDOR detection of a solvent-derived Ni-(OH(x))-Fe bridge that is lost upon activation of the hydrogenase from Desulfovibrio gigas, Jan 16. J Am Chem Soc. 124:281-6., Number 2 AbstractWebsite

Crystallographic studies of the hydrogenases (Hases) from Desulfovibrio gigas (Dg) and Desulfovibrio vulgaris Miyazaki (DvM) have revealed heterodinuclear nickel-iron active centers in both enzymes. The structures, which represent the as-isolated (unready) Ni-A (S = (1)/(2)) enzyme state, disclose a nonprotein ligand (labeled as X) bridging the two metals. The bridging atom was suggested to be an oxygenic (O(2)(-) or OH(-)) species in Dg Hase and an inorganic sulfide in DvM Hase. To determine the nature and chemical characteristics of the Ni-X-Fe bridging ligand in Dg Hase, we have performed 35 GHz CW (17)O ENDOR measurements on the Ni-A form of the enzyme, exchanged into H(2)(17)O, on the active Ni-C (S = (1)/(2)) form prepared by H(2)-reduction of Ni-A in H(2)(17)O, and also on Ni-A formed by reoxidation of Ni-C in H(2)(17)O. In the native state of the protein (Ni-A), the bridging ligand does not exchange with the H(2)(17)O solvent. However, after a reduction/reoxidation cycle (Ni-A --> Ni-C --> Ni-A), an (17)O label is introduced at the active site, as seen by ENDOR. Detailed analysis of a 2-D field-frequency plot of ENDOR spectra taken across the EPR envelope of Ni-A((17)O) shows that the incorporated (17)O has a roughly axial hyperfine tensor, A((17)O) approximately [5, 7, 20] MHz, discloses its orientation relative to the g tensor, and also yields an estimate of the quadrupole tensor. The substantial isotropic component (a(iso)((17)O) approximately 11 MHz) of the hyperfine interaction indicates that a solvent-derived (17)O is indeed a ligand to Ni and thus that the bridging ligand X in the Ni-A state of Dg Hase is indeed an oxygenic (O(2)(-) or OH(-)) species; comparison with earlier EPR results by others indicates that the same holds for Ni-B. The small (57)Fe hyperfine coupling seen previously for Ni-A (A((57)Fe) approximately 0.9 MHz) is now shown to persist in Ni-C, A((57)Fe) approximately 0.8 MHz. However, the (17)O signal is lost upon reductive activation to the Ni-C state; reoxidation to Ni-A leads to the reappearance of the signal. Consideration of the electronic structure of the EPR-active states of the dinuclear center leads us to suggest that the oxygenic bridge in Ni-A(B) is lost in Ni-C and is re-formed from solvent upon reoxidation to Ni-A. This implies that the reductive activation to Ni-C opens Ni/Fe coordination sites which may play a central role in the enzyme's activity.

Chen, P, DeBeer George S, Cabrito I, Antholine WE, Moura JJ, Moura I, Hedman B, Hodgson KO, Solomon EI.  2002.  Electronic structure description of the mu(4)-sulfide bridged tetranuclear Cu(Z) center in N(2)O reductase, Feb 6. J Am Chem Soc. 124:744-5., Number 5 AbstractWebsite

Spectroscopy coupled with density functional calculations has been used to define the spin state, oxidation states, spin distribution, and ground state wave function of the mu4-sulfide bridged tetranuclear CuZ cluster of nitrous oxide reductase. Initial insight into the electronic contribution to N2O reduction is developed, which involves a sigma superexchange pathway through the bridging sulfide.

Raaijmakers, H, Macieira S, Dias JM, Teixeira S, Bursakov S, Huber R, Moura JJG, Moura I, Romao MJ.  2002.  Gene sequence and the 1.8 angstrom crystal structure of the tungsten-containing formate dehydrogenase from Desulfolvibrio gigas. Structure. 10:1261-1272., Number 9 AbstractWebsite
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