Export 2155 results:
Sort by: Author Title Type [ Year  (Desc)]
1998
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
Stalhandske, CMV, Dong J, Tavares P, Liu MY, Legall J, Moura JJG, Moura I, Park JB, Adams MWW, Scott RA.  1998.  Probing the iron environment in desulforedoxin. EXAFS of oxidized and reduced states. INORGANICA CHIMICA ACTA. {273}:{409-411}., Number {1-2} Abstract

Fe XAS data were collected on the oxidized and reduced forms of desulforedoxin from Desulfovibrio gigas, the oxidized form of rubredoxin from Clostridium pasteurianum, and the reduced form of rubredoxin from Pyrococcus furiosus. Analysis of these data is consistent with tetrahedral FeS(4) coordination in both oxidation states, and an expansion of the Fe-S distances from 2.27 to 2.33 Angstrom upon reduction. (C) 1998 Elsevier Science S.A. All rights reserved.

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.

1997
Devreese, B, Costa C, Demol H, Papaefthymiou V, Moura I, Moura JJ, Van Beeumen J.  1997.  The primary structure of the split-Soret cytochrome c from Desulfovibrio desulfuricans ATCC 27774 reveals an unusual type of diheme cytochrome c, Sep 1. Eur J Biochem. 248:445-51., Number 2 AbstractWebsite

The complete amino acid sequence of the unusual diheme split-Soret cytochrome c from the sulphate-reducing Desulfovibrio desulfuricans strain ATCC 27774 has been determined using classical chemical sequencing techniques and mass spectrometry. The 247-residue sequence shows almost no similarity with any other known diheme cytochrome c, but the heme-binding site of the protein is similar to that of the cytochromes c3 from the sulphate reducers. The cytochrome-c-like domain of the protein covers only the C-terminal part of the molecule, and there is evidence for at least one more domain containing four cysteine residues, which might bind another cofactor, possibly a non-heme iron-containing cluster. This domain is similar to a sequence fragment of the genome of Archaeoglobus fulgidus, which confirms the high conservation of the genes involved in sulfate reduction.

Bursakov, SA, Carneiro C, Almendra MJ, Duarte RO, Caldeira J, Moura I, Moura JJ.  1997.  Enzymatic properties and effect of ionic strength on periplasmic nitrate reductase (NAP) from Desulfovibrio desulfuricans ATCC 27774, Oct 29. Biochem Biophys Res Commun. 239:816-22., Number 3 AbstractWebsite

Some sulfate reducing bacteria can induce nitrate reductase when grown on nitrate containing media being involved in dissimilatory reduction of nitrate, an important step of the nitrogen cycle. Previously, it was reported the purification of the first soluble nitrate reductase from a sulfate-reducing bacteria Desulfovibrio desulfuricans ATCC 27774 (S.A. Bursakov, M.-Y. Liu, W.J. Payne, J. LeGall, I. Moura, and J.J.G. Moura (1995) Anaerobe 1, 55-60). The present work provides further information about this monomeric periplasmic nitrate reductase (Dd NAP). It has a molecular mass of 74 kDa, 18.6 U specific activity, KM (nitrate) = 32 microM and a pHopt in the range 8-9.5. Dd NAP has peculiar properties relatively to ionic strength and cation/anion activity responses. It is shown that monovalent cations (potassium and sodium) stimulate NAP activity and divalent (magnesium and calcium) inhibited it. Sulfate anion also acts as an activator in KPB buffer. NAP native form is protected by phosphate anion from cyanide inactivation. In the presence of phosphate, cyanide even stimulates NAP activity (up to 15 mM). This effect was used in the purification procedure to differentiate between nitrate and nitrite reductase activities, since the later is effectively blocked by cyanide. Ferricyanide has an inhibitory effect at concentrations higher than 1 mM. The N-terminal amino acid sequence has a cysteine motive C-X2-C-X3-C that is most probably involved in the coordination of the [4Fe-4S] center detected by EPR spectroscopy. The active site of the enzyme consists in a molybdopterin, which is capable for the activation of apo-nit-1 nitrate reductase of Neurospora crassa. The oxidized product of the pterin cofactor obtained by acidic hidrolysis of native NAP with sulfuric acid was identified by HPLC chromatography and characterized as a molybdopterin guanine dinucleotide (MGD).

Huyett, JE, Carepo M, Pamplona A, Franco R, Moura I, Moura JJG, Hoffman BM.  1997.  Fe-57 Q-band pulsed ENDOR of the hetero-dinuclear site of nickel hydrogenase: Comparison of the NiA, NiB, and NiC states, Oct 1. Journal of the American Chemical Society. 119:9291-9292., Number 39 AbstractWebsite
n/a
Moura, I, Bursakov S, Costa C, Moura JJ.  1997.  Nitrate and nitrite utilization in sulfate-reducing bacteria, Oct. Anaerobe. 3:279-90., Number 5 AbstractWebsite
n/a
Andrade, S, Kamenskaya EO, Levashov AV, Moura JJ.  1997.  Encapsulation of flavodoxin in reverse micelles, May 29. Biochem Biophys Res Commun. 234:651-4., Number 3 AbstractWebsite

The regulation of the properties of Desulfovibrio gigas flavodoxin in AOT/water/iso-octane micellar system was studied. UV-visible spectroscopic studies have shown that photoreduction of flavodoxin in the presence of EDTA leads to hydroquinone formation through the intermediate semiquinone. The [free FMN] - [bound to flavodoxin FMN] equilibrium (and hence, the amount of apoprotein) depends on redox state of FMN and on hydration degree which controls the micellar size. Thus, a new method of reversible cofactor removing under mild conditions (at low hydration degree of micelles) is suggested, accompained by isolation of apo-form of the protein.

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.

Costa, C, Teixeira M, Legall J, Moura JJG, Moura I.  1997.  Formate dehydrogenase from Desulfovibrio desulfuricans ATCC 27774: Isolation and spectroscopic characterization of the active sites (heme, iron-sulfur centers and molybdenum), Apr. Journal of Biological Inorganic Chemistry. 2:198-208., Number 2 AbstractWebsite

An air-stable formate dehydrogenase, an enzyme that catalyzes the oxidation of formate to CO2, was purified from a sulfate-reducing organism, Desulfovibrio desulfuricans ATCC 27774. The enzyme has a molecular mass of approximately 150 kDa (three different subunits: 88, 29 and 16 kDa) and contains three types of redox-active centers: four c-type hemes, nonheme iron arranged as two [4Fe-4S](2+/1+) centers and a molybdenum-pterin site. Selenium was also chemically detected. The enzyme specific activity is 78 units per mg of protein. Mo(V) EPR signals were observed in the native, reduced and formate-reacted states. EPR signals related to the presence of multiple low-spin hemes were also observed in the oxidized state. Upon reduction, an examination of the EPR data under appropriate conditions distinguishes two types of iron-sulfur centers, an [Fe-S] center I (g(max)=2.050, g(med)=1.947, g(min)=1.896) and an [Fe-S] center II (g(max)=2.071, g(med)=1.926, g(min)=1.865). Mossbauer spectroscopy confirmed the presence of four hemes in the low-spin state. The presence of two [4Fe-4S](2+/1+) centers was confirmed, one of these displaying very small hyperfine coupling constants in the +1 oxidation state. The midpoint redox potentials of the enzyme metal centers were also estimated.

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.

Pina, F, Parola AJ, SaintMaurice A, Manfrin MF, Moggi L, Indelli T, Scandola F.  1997.  Electron transfer between Fe(CN)(6)(3-) and iodide promoted by supercomplexation with a polyammonium macrocycle, 1997. Journal of the Chemical Society-Dalton Transactions. :2327-2330. AbstractWebsite

Some new properties promoted by the formation of a supercomplex between iron hexacyanometallates and the polyazamacrocycle [32]aneN(8) (1,5,9,13,17,21,25,29-octaazacyclodotrane) are described. In the presence of the polyazamacrocycle, thermal and photoinduced electron transfer from iodide to Fe(CN)(6)(3-) were observed in moderately acidic media. The thermal reaction is slow (k(obs) = 8.9 x 10(-4) s(-1), at 25 degrees C) and proceeds to an equilibrium (K = 7 M-2, at 25 degrees C). The reaction is almost isoergonic, with favorable enthalpy and unfavorable entropy changes (Delta G degrees = -4.8 kJ mol(-1), Delta H degrees = -160 kJ mol(-1), Delta S degrees = -0.54 kJ mol(-1) K-1). A photoinduced electron-transfer process, leading to additional iodide oxidation, was observed upon flash irradiation of equilibrated solutions. Following the photoinduced process, the system reverts to the thermal equilibrium in the dark. The promoting role of the macrocycle is thermodynamic for the thermal process (anodic shift in the Fe-II/III potential upon supercomplex formation) and kinetic for the photoinduced process [formation of ion-paired species between hexacyanoferrate(III) and iodide upon supercomplex formation]. The thermal reaction is reversible in basic media (where the macrocycle deprotonates and supercomplex formation is prevented), providing an example of on/off switching by pH changes of an electron-transfer reaction.

Pina, F, Benedito L, Melo JM, Parola AJ, Lima JC, Macanita AL.  1997.  Structural transformations of the synthetic salt 4',7-dihydroxyflavylium chloride in acid and basic aqueous solutions .1. Ground state, 1997. Anales De Quimica. 93:111-118. AbstractWebsite

A complete study of the structural pH dependent transformations of the synthetic flavylium salt 4',7-dihydroxyflavylium chloride (DHF), occurring in aqueous solutions, including the basic region, is described. The kinetic study of the transformations occurring in acidic media (quinoidal base (A) reversible arrow flavylium cation (AH(+)) reversible arrow hemiacetal (B) reversible arrow cis-chalone (C-cis) reversible arrow trans-chalcone (C-trans)) allowed to conclude that the cis-trans isomerization is faster than the tautomerization and the hydration processes, which is unique in the anthocyanins family. Results obtained with the parent compound 4'7-dimethoxyglavylium chloride (DMF) with relevance to this study are also presented. In equilibrated basic solution the existence of acid-base equilibria involving the trans-Chalcone (C-trans) and its conjugated bases, (C-trans(-) and C-trans(2)), was detected. Freshly prepared solutions at pH >7 show also the presence of a transient species identified as the ionized quinoidal base (A(-)), which is almost completely converted into C-trans(2-) with a pH dependent rate constant.

Coito, F, Lemos JM, Silva RN, Mosca E.  1997.  Adaptive control of a solar energy plant: Exploiting accessible disturbances. International journal of adaptive control and signal processing. 11:327–342(Number 4: Wiley Online Library ) Abstract

n/a

Coito, F, Lemos JM, Silva RN, Mosca E.  1997.  Adaptive control of a solar energy plant: Exploiting accessible disturbances. International journal of adaptive control and signal processing. 11:327–342., Number 4: Wiley Online Library 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.

Maestri, M, Ballardini R, Pina F, Melo MJ.  1997.  An easy and inexpensive flash spectroscopy experiment. Journal of Chemical Education. 74:1314-1316., Number 11 AbstractWebsite
n/a
Pina, F, Melo MJ, Ballardini R, Flamigni L, Maestri M.  1997.  Flash photolysis of 4',7-dihydroxyflavylium perchlorate. New Journal of Chemistry. 21:969-976., Number 9 AbstractWebsite
n/a
Pina, F, Melo MJ, Maestri M, Ballardini R, Balzani V.  1997.  Photochromism of 4'-methoxyflavylium perchlorate. A ''write-lock-read-unlock-erase'' molecular switching system. Journal of the American Chemical Society. 119:5556-5561., Number 24 AbstractWebsite
n/a
Romao, MJ, Knablein J, Huber R, Moura JJ.  1997.  Structure and function of molybdopterin containing enzymes. Prog Biophys Mol Biol. 68:121-44., Number 2-3 AbstractWebsite

Molybdopterin containing enzymes are present in a wide range of living systems and have been known for several decades. However, only in the past two years have the first crystal structures been reported for this type of enzyme. This has represented a major breakthrough in this field. The enzymes share common structural features, but reveal different polypeptide folding topologies. In this review we give an account of the related spectroscopic information and the crystallographic results, with emphasis on structure-function studies.

Romao, MJ, Knablein J, Huber R, Moura JJG.  1997.  Structure and function of molybdopterin containing enzymes. Progress in Biophysics & Molecular Biology. 68:121-144., Number 2-3 AbstractWebsite
n/a
1996
Marques, F, Duarte RO, Moura JJ, Bicho MP.  1996.  Conversion of adrenaline to indolic derivatives by the human erythrocyte plasma membrane, Sep-Oct. Biol Signals. 5:275-82., Number 5 AbstractWebsite

The conversion of adrenaline to aminochromes by the human erythrocyte plasma membranes at pH 9.5 was shown to be a complex reaction that proceeded at least by two distinct phases. The first one, corresponding to the formation of adrenochrome, is catalyzed in the presence of the membranes, suggesting the involvement of an enzyme-mediated process. Active oxygen species were identified as intermediates during this phase. Oxygen radical scavengers (catalase and superoxide dismutase) suggested H2O2 and O2- involvement. Adrenochrome formation was stimulated by NADH indicating the participation of another enzyme (NADH dehydrogenase) which is known to be present in the human erythrocyte plasma membrane. The second phase, corresponding to the disappearance of adrenochrome, is also stimulated by NADH and inhibited in the presence of the membranes. In this reaction, adrenochrome is converted to aminochromes via adrenochrome semiquinone. The formation of radical species is demonstrated by EPR spectroscopy. The results led to the proposal of a mechanism for the formation of adrenochrome and other oxidation products from adrenaline.

Costa, C, Moura JJ, Moura I, Wang Y, Huynh BH.  1996.  Redox properties of cytochrome c nitrite reductase from Desulfovibrio desulfuricans ATCC 27774, Sep 20. J Biol Chem. 271:23191-6., Number 38 AbstractWebsite

The dissimilatory nitrite reductase from Desulfovibrio desulfuricans ATCC 27774 catalyzes the reduction of nitrite to ammonia. Previous spectroscopic investigation revealed that it is a hexaheme cytochrome containing one high spin ferric heme and five low spin ferric hemes in the oxidized enzyme. The current study uses the high resolution of Mossbauer spectroscopy to obtain redox properties of the six heme groups. Correlating the Mossbauer findings with the EPR data reveals the pairwise spin-spin coupling among four of the heme groups. The other two hemes are found to be magnetically isolated. Reduction with dithionite and reaction with CO further indicate that only the high spin heme is capable of binding small exogenous ligands. These results confirm our previous finding that Desulfovibrio desulfuricans nitrite reductase contains six heme groups and that the high spin ferric heme is the substrate and inhibitor binding site.

Lloyd, SG, Franco R, Moura JJG, Moura I, Ferreira GC, Huynh BH.  1996.  Functional necessity and physicochemical characteristics of the 2Fe-2S cluster in mammalian ferrochelatase, Oct 16. Journal of the American Chemical Society. 118:9892-9900., Number 41 AbstractWebsite

The recently discovered [2Fe-2S] cluster in mouse liver ferrochelatase has been characterized using UV-vis, EPR, and Mossbauer spectroscopic techniques. Studies are reported here for the recombinant protein purified from an overproducing transformed Escherichia coli strain. A positive correlation is observed between the presence of the [2Fe-2S] cluster and the enzymatic specific activity and demonstrates the necessity of this cofactor. Chemical analysis revealed that the preparations contained up to 1.3 Fe/molecule and indicated a 1:1 stoichiometry between Fe and acid-labile sulfide. The [2Fe-2S] cluster in the as-isolated ferrochelatase exhibits a UV-vis spectrum indicative of a [2Fe-2S](2+) cluster and is EPR-silent. The 8 T Mossbauer spectrum of the Fe-57-enriched as-isolated protein is well simulated by parameters Delta E(Q) = 0.69 +/- 0.03 mm/s and delta = 0.28 +/- 0.02 mm/s and confirms the presence of a diamagnetic ground state. Upon reduction with sodium dithionite, ferrochelatase shows a near-axial EPR spectrum with g-values of 2.00, 1.93, and 1.91, consistent with a S = 1/2 mixed valent Fe3+-Fe2+ cluster. The Orbach temperature dependence of the EPR line widths was used to provide an estimate of the exchange coupling J, which was determined to be on the order of 500-650 cm(-1) (+JS(1) . S-2 model). Redox titrations monitored by UV-vis and EPR spectroscopy revealed midpoint potentials of -390 +/- 10 and -405 +/- 10 mV, respectively. Mossbauer spectra of the sodium dithionite-reduced Fe-57-enriched ferrochelatase collected at 4.2 K in the presence of magnetic fields of 60 mT and 8 T strengths were analyzed in the mixed-valent S = 1/2 ground state. Parameters for the ferric site are Delta E(Q) = 1.2 +/- 0.2 mm/s and delta = 0.28 +/- 0.03 mm/s, with somewhat anisotropic hyperfine splittings; for the ferrous site, Delta E(Q) = 3.3 +/- 0.1 mm/s and delta = 0.67 +/- 0.04 mm/s with anisotropic hyperfine splittings characteristic of high-spin ferrous ion. The similarities and differences with other characterized [2Fe-2S](+) cluster-containing proteins are discussed.

loading