Export 1423 results:
Sort by: Author Title Type [ Year  (Desc)]
1999
Bazzicalupi, C, Bencini A, Bianchi A, Giorgi C, Fusi V, Valtancoli B, Bernardo MA, Pina F.  1999.  Effect of protonation and Zn(II) coordination on the fluorescence emission of a phenanthroline-containing macrocycle. An unusual case of "nonemissive'' Zn(II) complex. Inorganic Chemistry. 38:3806-3813., Number 17 AbstractWebsite
n/a
Bencini, A, Bernardo MA, Bianchi A, Fusi V, Giorgi C, Pina F, Valtancoli B.  1999.  Macrocyclic polyamines containing phenanthroline moieties - Fluorescent chemosensors for H+ and Zn2+ ions. European Journal of Inorganic Chemistry. :1911-1918., Number 11 AbstractWebsite
n/a
Ciampolini, M, Formica M, Fusi V, Saint-Mauricec A, Micheloni M, Nardi N, Pontellini R, Pina F, Romani P, Sabatini AM, Valtancoli B.  1999.  Selective lithium complexation by photoactive aza-cages bearing the anthracene function. European Journal of Inorganic Chemistry. :2261-2268., Number 12 AbstractWebsite
n/a
Franco, R, Ma JG, Lu Y, Pereira A, Tavares P, Moura I, Shelnutt JA, Ferreira GC.  1999.  Spectroscopic characterization of porphyrin binding to ferrochelatase, the last enzyme in the heme biosynthetic pathway. Journal Of Inorganic Biochemistry. {74}:{130}., Number {1-4} Abstract
n/a
Schienstock, G, Bechmann G, Flecker J, Huws U, Van Hootegem G, Mirabile ML, Moniz A, Ò Siochru S.  1999.  Technical Systems, Organisation Forms and Social Implications: Statistical Analysis of the Firm Survey (Second Interim Report). , Number 5883: University Library of Munich, Germany Abstract

This is the second interim report of the research project "Information Society, Work and the Generation of New Forms of Social Exclusion" (SOWING). It is based on a firm survey conducted in the eight regions participating in the research project — Flanders (Belgium), Lazio (Italy), Niederösterreich (Austria), Portugal, the Republic of Ireland, the Stuttgart area (Germany), the Tampere region (Finland) and the West London area (U.K.). The aim of this report is to present a broad overview of the collected data. In general, only simple statistical methods have been applied. The report focuses on a regional comparison; however, the data have also been analysed by firm size, measured by quantity of staff, and industrial sector. It should be seen as a first step in the data analysis; it may also give some hints for a more strategic analysis of the survey data.

Schienstock, G, Bechmann G, Flecker J, Huws U, Van Hootegem G, Mirabile ML, Moniz A, Ò Siochru S.  1999.  {Technical Systems, Organisation Forms and Social Implications: Statistical Analysis of the Firm Survey (Second Interim Report)}. , Number 5883: University Library of Munich, Germany Abstract

This is the second interim report of the research project "Information Society, Work and the Generation of New Forms of Social Exclusion" (SOWING). It is based on a firm survey conducted in the eight regions participating in the research project — Flanders (Belgium), Lazio (Italy), Niederösterreich (Austria), Portugal, the Republic of Ireland, the Stuttgart area (Germany), the Tampere region (Finland) and the West London area (U.K.). The aim of this report is to present a broad overview of the collected data. In general, only simple statistical methods have been applied. The report focuses on a regional comparison; however, the data have also been analysed by firm size, measured by quantity of staff, and industrial sector. It should be seen as a first step in the data analysis; it may also give some hints for a more strategic analysis of the survey data.

1998
Ma, JG, Zhang J, Franco R, Jia SL, Moura I, Moura JJ, Kroneck PM, Shelnutt JA.  1998.  The structural origin of nonplanar heme distortions in tetraheme ferricytochromes c3, Sep 8. Biochemistry. 37:12431-42., Number 36 AbstractWebsite

Resonance Raman (RR) spectroscopy, molecular mechanics (MM) calculations, and normal-coordinate structural decomposition (NSD) have been used to investigate the conformational differences in the hemes in ferricytochromes c3. NSD analyses of heme structures obtained from X-ray crystallography and MM calculations of heme-peptide fragments of the cytochromes c3 indicate that the nonplanarity of the hemes is largely controlled by a fingerprint peptide segment consisting of two heme-linked cysteines, the amino acids between the cysteines, and the proximal histidine ligand. Additional interactions between the heme and the distal histidine ligand and between the heme propionates and the protein also influence the heme conformation, but to a lesser extent than the fingerprint peptide segment. In addition, factors that influence the folding pattern of the fingerprint peptide segment may have an effect on the heme conformation. Large heme structural differences between the baculatum cytochromes c3 and the other proteins are uncovered by the NSD procedure [Jentzen, W., Ma, J.-G., and Shelnutt, J. A. (1998) Biophys. J. 74, 753-763]. These heme differences are mainly associated with the deletion of two residues in the covalently linked segment of hemes 4 for the baculatum proteins. Furthermore, some of these structural differences are reflected in the RR spectra. For example, the frequencies of the structure-sensitive lines (nu4, nu3, and nu2) in the high-frequency region of the RR spectra are lower for the Desulfomicrobium baculatum cytochromes c3 (Norway 4 and 9974) than for the Desulfovibrio (D.) gigas, D. vulgaris, and D. desulfuricans strains, consistent with a more ruffled heme. Spectral decompositions of the nu3 and nu10 lines allow the assignment of the sublines to individual hemes and show that ruffling, not saddling, is the dominant factor influencing the frequencies of the structure-sensitive Raman lines. The distinctive spectra of the baculatum strains investigated are a consequence of hemes 2 and 4 being more ruffled than is typical of the other proteins.

Flomen, {RH }, Vatcheva R, Gorman {PA }, Baptista {PMRV}, Groet J.  1998.  Construction and analysis of a sequence-ready map in 4q25: Rieger syndrome can be caused by haploinsufficiency of RIEG, but also by chromosome breaks approximate to 90 kb upstream of this gene, feb. Genomics. 47:409–413., Number 3: Elsevier Abstract

The autosomal dominant disorder Rieger syndrome (RIEG) shows genetic heterogeneity and has a phenotype characterized by malformations of the anterior segment of the eye, failure of the periumbilical skin to involute, and dental hypoplasia. The main locus for RIEG was mapped to the 4q25-q27 chromosomal segment using a series of cytogenetic abnormalities as well as by genetic linkage to DNA markers. Recently, a bicoid-related homeobox transcription factor gene called RIEG has been cloned, characterized, and proven to cause the 4q25 linked RIEG. Its mode of action in the pathogenesis of RIEG was not conclusively proven, since most etiological mutations detected. In the RIEG sequence caused amino acid substitutions or splice changes in the homeodomain. Through FISH analysis of a 460-kb sequence-ready map (PAC contig) around RIEG that we report in this paper, we demonstrate that the 4q25 linked RIEG disorder can arise from the haploid, whole-gene deletion of RIEG, but also from a translocation break 90 kb upstream from the gene. The data provide conclusive evidence that physical or functional haploinsufficiency of RIEG is the pathogenic mechanism for Rieger syndrome. The map also defines restriction fragments bearing sequences with a potential key regulatory role in the control of homeobox gene expression.

Feio, MJ, Beech IB, Carepo M, Lopes JM, Cheung CW, Franco R, Guezennec J, Smith JR, Mitchell JI, Moura JJ, Lino AR.  1998.  Isolation and characterisation of a novel sulphate-reducing bacterium of the Desulfovibrio genus, Apr. Anaerobe. 4:117-30., Number 2 AbstractWebsite

A novel sulphate-reducing bacterium (Ind 1) was isolated from a biofilm removed from a severely corroded carbon steel structure in a marine environment. Light microscopy observations revealed that cells were Gram-negative, rod shaped and very motile. Partial 16S rRNA gene sequencing and analysis of the fatty acid profile demonstrated a strong similarity between the new species and members from the Desulfovibrio genus. This was confirmed by the results obtained following purification and characterisation of the key proteins involved in the sulphate-reduction pathway. Several metal-containing proteins, such as two periplasmic proteins: hydrogenase and cytochrome c3, and two cytoplasmic proteins: ferredoxin and sulphite reductase, were isolated and purified. The latter proved to be of the desulfoviridin type which is typical of the Desulfovibrio genus. The study of the remaining proteins revealed a high degree of similarity with the homologous proteins isolated from Desulfovibrio gigas. However, the position of the strain within the phylogenetic tree clearly indicates that the bacterium is closely related to Desulfovibrio gabonensis, and these three strains form a separate cluster in the delta subdivision of the Proteobacteria. On the basis of the results obtained, it is suggested that Ind 1 belongs to a new species of the genus Desulfovibrio, and the name Desulfovibrio indonensis is proposed.

Bencini, A, Bernardo MA, Bianchi A, Ciampolini M, Fusi V, Nardi N, Parola AJ, Pina F, Valtancoli B.  1998.  Modulation of the ligational properties of a new cylindrical macrotricycle by coupling of photochemical- and pH-switching properties, 1998. Journal of the Chemical Society-Perkin Transactions 2. :413-418. AbstractWebsite

The new cylindrical molecule L containing two tetraazamacrocyclic rings linked by two azobenzene pillars displays photoelastic properties, Light absorption at 366 nm gives rise to trans --> cis isomerization of the azobenzene moieties producing two isomers containing one or two cis-azobenzenes, respectively, The three trans-trans (E-E), trans-cis (E-Z) and cis-cis (Z-Z) isomers have been identified and characterized by H-1 NMR spectroscopy, allowing the dependence of their formation percentages with irradiation time to be determined, The sequence of photochemical reactions E-E --> E-Z --> Z-Z allows almost complete conversion of the E-E into the Z-Z isomer at 366 nm and 298 K, Both thermal (k = 1.75 x 10(-5) s(-1) at 313 K) and photo-induced (at 436 and 313 nm) back-isomerization reactions have been studied, The protonation constants of the three isomers in equimolar solutions of water-DMSO indicate a decreasing basicity in the order E-E > E-Z > Z-Z, in agreement with increasing electrostatic repulsion between the positive charges caused by a reduction in the separation between the protonation sites occurring upon Z --> E isomerization.

1997
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
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, 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
1996
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.

Gu, ZJ, Dong J, Allan CB, Choudhury SB, Franco R, Moura JJG, Legall J, Przybyla AE, Roseboom W, Albracht SPJ, Axley MJ, Scott RA, Maroney MJ.  1996.  Structure of the Ni sites in hydrogenases by X-ray absorption spectroscopy. Species variation and the effects of redox poise, Nov 13. Journal of the American Chemical Society. 118:11155-11165., Number 45 AbstractWebsite

Structural information obtained from the analysis of nickel K-edge X-ray absorption spectroscopic data of [NiFe]hydrogenases from Desulfovibrio gigas, Thiocapsa roseopersicina, Desulfovibrio desulfuricans (ATCC 27774), Escherichia coli (hydrogenase-1), Chromatium vinosum, and Alcaligenes eutrophus H16 (NAD(+)-reducing, soluble hydrogenase), poised in different redox states, is reported. The data allow the active-site structures of enzymes from several species to be compared, and allow the effects of redox poise on the structure of the nickel sites to be examined. In addition, the structure of the nickel site obtained from recent crystallographic studies of the D. gigas enzyme (Volbeda, A.; Charon, M.-H.; Piras, C.; Hatchikian, E. C.; Frey, M.; Fontecilla-Camps, J. C. Nature 1995, 373, 580-587) is compared with the structural features obtained from the analysis of XAS data from the same enzyme. The nickel sites of all but the oxidized (as isolated) sample of A. eutrophus hydrogenase are quite similar. The nickel K-edge energies shift 0.9-1.5 eV to lower energy upon reduction from oxidized (forms A and B) to fully reduced forms. This value is comparable with no more than a one-electron metal-centered oxidation state change. With the exception of T. roseopersicina hydrogenase, most of the edge energy shift (-0.8 eV) occurs upon reduction of the oxidized enzymes to the EPR-silent intermediate redox level (SI). Analysis of the XANES features assigned to 1s-->3d electronic transitions indicates that the shift in energy that occurs for reduction of the enzymes to the SI level may be attributed at least in part to an increase in the coordination number from five to six. The smallest edge energy shift is observed for the T. roseopersicina enzyme, where the XANES data indicate that the nickel center is always six-coordinate. With the exception of the oxidized sample of A. eutrophus hydrogenase, the EXAFS data are dominated by scattering from S-donor ligands at similar to 2.2 Angstrom. The enzyme obtained from T. roseopersicina also shows evidence for the presence of O,N-donor ligands. The data from A. eutrophus hydrogenase are unique in that they indicate that a significant structural change occurs upon reduction of the enzyme. EXAFS data obtained from the oxidized (as isolated) A. eutrophus enzyme indicate that the EXAFS is dominated by scattering from 3-4 N,O-donor atoms at 2.06(2) Angstrom, with contributions from 2-3 S-donor ligands at 2.35(2) Angstrom. This changes upon reduction to a more typical nickel site composed of similar to 4 S-donor ligands at a Ni-S distance of 2.19(2) Angstrom. Evidence for the presence of atoms in the 2.4-2.9 Angstrom distance range is found in most samples, particularly the reduced enzymes (SI, form C, and R). The analysis of these data is complicated by the fact that it is difficult to distinguish between S and Fe scattering atoms at this distance, and by the potential presence of both S and another metal atom at similar distances. The results of EXAFS analysis are shown to be in general agreement with the published crystal structure of the D. gigas enzyme.

Coelho, AV, Matias PM, Carrondo MA, Tavares P, Moura JJ, Moura I, Fulop V, Hajdu J, Legall J.  1996.  Preliminary crystallographic analysis of the oxidized form of a two mono-nuclear iron centres protein from Desulfovibrio desulfuricans ATCC 27774, Jun. Protein Sci. 5:1189-91., Number 6 AbstractWebsite

Crystals of the fully oxidized form of desulfoferrodoxin were obtained by vapor diffusion from a solution containing 20% PEG 4000, 0.1 M HEPES buffer, pH 7.5, and 0.2 M CaCl2. Trigonal and/or rectangular prisms could be obtained, depending on the temperature used for the crystal growth. Trigonal prisms belong to the rhombohedral space group R32, with a = 112.5 A and c = 63.2 A; rectangular prisms belong to the monoclinic space group C2, with a = 77.7 A, b = 80.9 A, c = 53.9 A, and beta = 98.1 degrees. The crystallographic asymmetric unit of the rhombohedral crystal form contains one molecule. There are two molecules in the asymmetric unit of the monoclinic form, in agreement with the self-rotation function.

Coelho, AV, Matias PM, Carrondo MA, Tavares P, Moura JJG, Moura I, Fulop V, Hajdu J, Legall J.  1996.  Preliminary crystallographic analysis of the oxidized form of a two mono-nuclear iron centres protein from Desulfovibrio desulfuricans ATCC 27774, Jul. PROTEIN SCIENCE. {5}:{1189-1191}., Number {6} Abstract

Crystals of the fully oxidized form of desulfoferrodoxin were obtained by vapor diffusion from a solution containing 20% PEG 4000, 0.1 M HEPES buffer, pH 7.5, and 0.2 M CaCl2. Trigonal and/or rectangular prisms could be obtained, depending on the temperature used for the crystal growth. Trigonal prisms belong to the rhombohedral space group R32, with a = 112.5 Angstrom and c = 63.2 Angstrom; rectangular prisms belong to the monoclinic space group C2, with a = 77.7 Angstrom, b = 80.9 Angstrom, c = 53.9 Angstrom, and beta = 98.1 degrees. The crystallographic asymmetric unit of the rhombohedral crystal form contains one molecule. There are two molecules in the asymmetric unit of the monoclinic form, in agreement with the self-rotation function.

Macedo, AL, Besson S, Moreno C, Fauque G, Moura JJ, Moura I.  1996.  Characterization of a 7Fe ferredoxin isolated from the marine denitrifier Pseudomonas nautica strain 617: spectroscopic and electrochemical studies, Dec 13. Biochem Biophys Res Commun. 229:524-30., Number 2 AbstractWebsite

A 7Fe ferredoxin, isolated from the marine denitrifier Pseudomonas nautica strain 617, was characterized. The NH2-terminal sequence analysis, performed until residue number 56, shows a high similarity with the 7Fe ferredoxins isolated from Azotobacter vinelandii, Pseudomonas putida, and Pseudomonas stutzeri. EPR and NMR spectroscopies identify the presence of both [3Fe-4S] and [4Fe-4S] clusters, with cysteinyl coordination. The electrochemical studies on [Fe-S] clusters show that a fast diffusion-dominated electron transfer, promoted by Mg(II), takes place between the ferredoxin and the glassy carbon electrode. Square wave voltammetry studies gave access to the electrosynthesis of a 4Fe center formed within the [3Fe-4S] core. The [3Fe-4S] cluster exhibited two reduction potentials at -175 and -680 +/- 10 mV and the [4Fe-4S] cluster was characterized by an unusually low reduction potential of -715 +/- 10 mV, at pH 7.6

Caldeira, J, Feicht R, White H, Teixeira M, Moura JJ, Simon H, Moura I.  1996.  EPR and Mossbauer spectroscopic studies on enoate reductase, Aug 2. J Biol Chem. 271:18743-8., Number 31 AbstractWebsite

Enoate reductase (EC 1.3.1.31) is a protein isolated from Clostridium tyrobutyricum that contains iron, labile sulfide, FAD, and FMN. The enzyme reduces the alpha,beta carbon-carbon double bond of nonactivated 2-enoates and in a reversible way that of 2-enals at the expense of NADH or reduced methyl viologen. UV-visible and EPR potentiometric titrations detect a semiquinone species in redox intermediate states characterized by an isotropic EPR signal at g = 2.0 without contribution at 580 nm. EPR redox titration shows two widely spread mid-point redox potentials (-190 and -350 mV at pH 7. 0), and a nearly stoichiometric amount of this species is detected. The data suggest the semiquinone radical has an anionic nature. In the reduced form, the [Fe-S] moiety is characterized by a single rhombic EPR spectrum, observed in a wide range of temperatures (4. 2-60 K) with g values at 2.013, 1.943, and 1.860 (-180 mV at pH 7.0). The gmax value is low when compared with what has been reported for other iron-sulfur clusters. Mossbauer studies reveal the presence of a [4Fe-4S]+2/+1 center. One of the subcomponents of the spectrum shows an unusually large value of quadrupole splitting (ferrous character) in both the oxidized and reduced states. Substrate binding to the reduced enzyme induces subtle changes in the spectroscopic Mossbauer parameters. The Mossbauer data together with known kinetic information suggest the involvement of this iron-sulfur center in the enzyme mechanism.

Pereira, AS, Franco R, Feio MJ, Pinto C, Lampreia J, Reis MA, Calvete J, Moura I, Beech I, Lino AR, Moura JJ.  1996.  Characterization of representative enzymes from a sulfate reducing bacterium implicated in the corrosion of steel, Apr 16. Biochem Biophys Res Commun. 221:414-21., Number 2 AbstractWebsite

This communication reports the isolation, purification and characterization of key enzymes involved in dissimilatory sulfate reduction of a sulfate reducing bacterium classified as Desulfovibrio desulfuricans subspecies desulfuricans New Jersey (NCIMB 8313) (Ddd NJ). The chosen strain, originally recovered from a corroding cast iron heat exchanger, was grown in large scale batch cultures. Physico-chemical and spectroscopic studies of the purified enzymes were carried out. These analyses revealed a high degree of similarity between proteins isolated from the DddNJ strain and the homologous proteins obtained from Desulfomicrobium baculatus Norway 4. In view of the results obtained, taxonomic reclassification of Desulfovibrio desulfuricans subspecies desulfuricans New Jersey (NCIMB 8313) into Desulfomicrobium baculatus (New Jersey) is proposed.

Parola, AJ, Pina F, Ferreira E, Maestri M, Balzani V.  1996.  Photoinduced electron- and energy-transfer processes of biacetyl imprisoned in a hemicarcerand, 1996. Journal of the American Chemical Society. 118:11610-11616. AbstractWebsite

The energy- and electron-transfer quenching processes of the lowest triplet excited state of biacetyl (2,3-butanedione) imprisoned in a hemicarcerand have been systematically investigated in CH2Cl2 solution at room temperature. Twenty potential quenchers have been used, including ten triplet energy accepters (mostly, aromatic hydrocarbons) and nine electron donors (mostly, aromatic amines). Bimolecular rate constants for the quenching processes were obtained by Stern-Volmer analysis and compared with those found for the quenching of free biacetyl. In the electron-transfer processes, aromatic amines with oxidation potential from +0.015 V (N,N,N',N'-tetramethyl-p-phenylenediamine) to +0.83 V (diphenylamine) quench free biacetyl at the diffusion-controlled limit, whereas for imprisoned biacetyl the rate constant decreases (roughly in a linear manner) from 4.0 x 10(8) to 1.2 x 10(5) M(-1) s(-1) As far as energy-transfer is concerned, the rate constant for the quenching of free biacetyl increases with decreasing Delta G degrees and reaches the diffusion-controlled plateau value (k(q) similar to 10(10) M(-1) s(-1)) for Delta G degrees similar to 0.1 eV, whereas for imprisoned biacetyl a scattered, bell-shaped log k(q) vs Delta G degrees plot is obtained, with a maximum value (similar to 10(6) M(-1) s(-1)) much below the diffusion-controlled limit. The results obtained show that the walls of the hemicarcerand allow only very weak electronic interaction between incarcerated triplet biacetyl and external quenchers. A brief discussion of the results obtained in the light of current energy- and electron-transfer theories is presented.

Dionísio, M, Ramos MJJ, Fernandes A.  1996.  Dielectric Studies on the miscibility in poly(vinyl acette)/poly(ethyl methacrylate) blends. Journal of Applied Polymer Science. 60:903-909.Website
Pereira, AS, Franco R, Feio MJ, Pinto C, Lampreia J, Reis MA, Calvete J, Moura I, Beech I, Lino AR, Moura JJG.  1996.  Characterization of representative enzymes from a sulfate reducing bacterium implicated in the corrosion of steel. Biochemical And Biophysical Research Communications. {221}:{414-421}., Number {2}, 525 B ST, STE 1900, SAN DIEGO, CA 92101-4495: ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS Abstract

This communication reports the isolation, purification and characterization of key enzymes involved in dissimilatory sulfate reduction of a sulfate reducing bacterium classified as Desulfovibrio desulfuricans subspecies desulfuricans New Jersey (NCIMB 8313) (Ddd NJ). The chosen strain, originally recovered from a corroding cast iron heat exchanger, was grown in large scale batch cultures. Physico-chemical and spectroscopic studies of the purified enzymes were carried out. These analyses revealed a high degree of similarity between proteins isolated from the DddNJ strain and the homologous proteins obtained from Desulfomicrobium baculatus Norway 4. In view of the results obtained, taxonomic reclassification of Desulfovibrio desulfuricans subspecies desulfuricans New Jersey (NCIMB 8313) into Desulfomicrobium baculatus (New Jersey) is proposed. (C) 1996 Academic Press, Inc.

1995
Morais, J, Palma PN, Frazao C, Caldeira J, Legall J, Moura I, Moura JJ, Carrondo MA.  1995.  Structure of the tetraheme cytochrome from Desulfovibrio desulfuricans ATCC 27774: X-ray diffraction and electron paramagnetic resonance studies, Oct 3. Biochemistry. 34:12830-41., Number 39 AbstractWebsite

The three-dimensional X-ray structure of cytochrome c3 from a sulfate reducing bacterium, Desulfovibrio desulfuricans ATCC 27774 (107 residues, 4 heme groups), has been determined by the method of molecular replacement [Frazao et al. (1994) Acta Crystallogr. D50, 233-236] and refined at 1.75 A to an R-factor of 17.8%. When compared with the homologous proteins isolated from Desulfovibrio gigas, Desulfovibrio vulgaris Hildenborough, Desulfovibrio vulgaris Miyazaki F, and Desulfomicrobium baculatus, the general outlines of the structure are essentialy kept [heme-heme distances, heme-heme angles, His-His (axial heme ligands) dihedral angles, and the geometry of the conserved aromatic residues]. The three-dimensional structure of D. desulfuricans ATCC 27774 cytochrome c3Dd was modeled on the basis of the crystal structures available and amino acid sequence comparisons within this homologous family of multiheme cytochromes [Palma et al. (1994) Biochemistry 33, 6394-6407]. This model is compared with the refined crystal structure now reported, in order to discuss the validity of structure prediction methods and critically evaluate the steps used to predict protein structures by homology modeling. The four heme midpoint redox potentials were determined by using deconvoluted electron paramagnetic resonance (EPR) redox titrations. Structural criteria (electrostatic potentials, heme ligand orientation, EPR g values, heme exposure, data from protein-protein interaction studies) are invoked to assign the redox potentials corresponding to each specific heme in the three-dimensional structure.

Franco, R, Moura JJ, Moura I, Lloyd SG, Huynh BH, Forbes WS, Ferreira GC.  1995.  Characterization of the iron-binding site in mammalian ferrochelatase by kinetic and Mossbauer methods, Nov 3. J Biol Chem. 270:26352-7., Number 44 AbstractWebsite

All organisms utilize ferrochelatase (protoheme ferrolyase, EC 4.99.1.1) to catalyze the terminal step of the heme biosynthetic pathway, which involves the insertion of ferrous ion into protoporphyrin IX. Kinetic methods and Mossbauer spectroscopy have been used in an effort to characterize the ferrous ion-binding active site of recombinant murine ferrochelatase. The kinetic studies indicate that dithiothreitol, a reducing agent commonly used in ferrochelatase activity assays, interferes with the enzymatic production of heme. Ferrochelatase specific activity values determined under strictly anaerobic conditions are much greater than those obtained for the same enzyme under aerobic conditions and in the presence of dithiothreitol. Mossbauer spectroscopy conclusively demonstrates that, under the commonly used assay conditions, dithiothreitol chelates ferrous ion and hence competes with the enzyme for binding the ferrous substrate. Mossbauer spectroscopy of ferrous ion incubated with ferrochelatase in the absence of dithiothreitol shows a somewhat broad quadrupole doublet. Spectral analysis indicates that when 0.1 mM Fe(II) is added to 1.75 mM ferrochelatase, the overwhelming majority of the added ferrous ion is bound to the protein. The spectroscopic parameters for this bound species are delta = 1.36 +/- 0.03 mm/s and delta EQ = 3.04 +/- 0.06 mm/s, distinct from the larger delta EQ of a control sample of Fe(II) in buffer only. The parameters for the bound species are consistent with an active site composed of nitrogenous/oxygenous ligands and inconsistent with the presence of sulfur ligands. This finding is in accord with the absence of conserved cysteines among the known ferrochelatase sequences. The implications these results have with regard to the mechanism of ferrochelatase activity are discussed.

loading