Export 1241 results:
Sort by: Author Title Type [ Year  (Desc)]
2003
Ricardo, CN, Inácio JA, Gerald JA, Ortigueira MD.  2003.  New BCH-Derived Sequences for CDMA Systems. 46th IEEE - Midwest Symposium on Circuits and Systems. :1255–1258. Abstract

New BCH-derived PN-EB (pseudo-noise even balanced) sequences suitable to be used in CDMA systems are presented in this paper. It is assumed a new definition for processing gain, which better accounts for the system performance regarding the narrow band noise rejection, and it is shown how to obtain high processing gain values, namely, by using zero mean spreading signals in channels with selective noise. The new sequences have low autocorrelation levels, exist in large numbers and can provide higher processing gain with selective noise.

Pessanha, M, Turner DL, Rothery EL, Pankhurst KL, Reid GA, Chapman SK, Xavier AV, Salgueiro CA.  2003.  NMR redox studies of flavocytochrome c3 from Shewanella frigidimarina. Inorganica Chimica Acta. 356:379-381. AbstractWebsite

Flavocytochrome c3 is a periplasmic fumarate reductase with Mr 63.8 kDa, isolated from Shewanella frigidimarina NCIMB400. NMR spectroscopy was tested for its potential to elucidate the oxidation profile of each of the four haem groups in the enzyme, using the strategy developed previously to perform the thermodynamic characterization of small tetrahaem cytochromes (FEBS Lett. 314 (1992) 155). This work shows that, despite the large size of the protein, 2D-NMR NOESY experiments can be used to obtain the network of chemical exchange connectivities, between the signals of specific haem groups in sequential oxidation stages.

Carvoeiras, P, Rodrigues MJ, A.G. B, Ortigueira MD.  2003.  A Prototype software for the Diagnostic of Atrial fibrillation. XXIV Congresso Português de Cardiologia and Revista Portuguesa de Cardiologia. III. Abstract

n/a

Pessanha, M, Louro RO, Correia IJ, Rothery EL, Pankhurst KL, Reid GA, Chapman SK, Turner DL, Salgueiro CA.  2003.  Thermodynamic characterization of a tetrahaem cytochrome isolated from a facultative aerobic bacterium, Shewanella frigidimarina: a putative redox model for flavocytochrome c3. Biochemical Journal. 370(Pt. 2):489-495. AbstractWebsite

The facultative aerobic bacterium Shewanella frigidimarina produces a small c-type tetrahaem cytochrome (86 residues) under anaerobic growth conditions. This protein is involved in the respiration of iron and shares 42% sequence identity with the N-terminal domain of a soluble flavocytochrome, isolated from the periplasm of the same bacterium, which also contains four c-type haem groups. The thermodynamic properties of the redox centres and of an ionizable centre in the tetrahaem cytochrome were determined using NMR and visible spectroscopy techniques. This is the first detailed thermodynamic study performed on a tetrahaem cytochrome isolated from a facultative aerobic bacterium and reveals that this protein presents unique features. The redox centres have negative and different redox potentials, which are modulated by redox interactions between the four haems (covering a range of 8–56mV) and by redox–Bohr interactions between the haems and an ionizable centre (-4 to -36mV) located in close proximity to haem III. All of the interactions between the five centres are clearly dominated by electrostatic effects and the microscopic reduction potential of haem III is the one most affected by the oxidation of the other haems and by the protonation state of the molecule. Altogether, this study indicates that the tetrahaem cytochrome isolated from S. frigidimarina (Sfc) has the thermodynamic properties to work as an electron wire between its redox partners. Considering the high degree of sequence identity between Sfc and the cytochrome domain of flavocytochrome c3, the structural similarities of the haem core, and that the macroscopic potentials are also identical, the results obtained in this work are rationalized in order to put forward a putative redox model for flavocytochrome c3.

Carvalho, AL, Dias FMV, Prates JAM, Nagy T, Gilbert HJ, Davies GJ, Ferreira LMA, Romao MJ, Fontes C.  2003.  Cellulosome assembly revealed by the crystal structure of the cohesin-dockerin complex. Proceedings of the National Academy of Sciences of the United States of America. 100:13809-13814., Number 24 AbstractWebsite
n/a
Moncada, MC, Moura S, Melo MJ, Roque A, Lodeiro C, Pina F.  2003.  Complexation of aluminum(III) by anthocyanins and synthetic flavylium salts - A source for blue and purple color. Inorganica Chimica Acta. 356:51-61. AbstractWebsite
n/a
Bonifácio, C, Cunha CA, Müller A, Timóteo CG, Dias JM, Moura I, Romão MJ.  2003.  Crystallization and preliminary X-ray diffraction analysis of the di-haem cytochrome c peroxidase from Pseudomonas stutzeri. Acta Crystallographica Section D. 59:345-347., Number 2: Munksgaard International Publishers AbstractWebsite
n/a
Bonifacio, C, Cunha CA, Muller A, Timoteo CG, Dias JM, Moura I, Romao MJ.  2003.  Crystallization and preliminary X-ray diffraction analysis of the di-haem cytochrome c peroxidase from Pseudomonas stutzeri. Acta Crystallographica Section D-Biological Crystallography. 59:345-347. AbstractWebsite
n/a
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
n/a
Auchere, F, Raleiras P, Benson L, Venyaminov SY, Tavares P, Moura JJG, Moura I, Rusnak F.  2003.  Formation of a stable cyano-bridged dinuclear iron cluster following oxidation of the superoxide reductases from Treponema pallidum and Desulfovibrio vulgaris with K3Fe(CN)(6). INORGANIC CHEMISTRY. {42}:{938-940}., Number {4} Abstract

Superoxide reductases catalyze the monovalent reduction of superoxide anion to hydrogen peroxide. Spectroscopic evidence for the formation of a dinuclear cyano-bridged adduct after K3Fe-(CN)(6) oxidation of the superoxide reductases neelaredoxin from Treponema pallidum and desulfoferrodoxin from Desulfovibrio vulgaris was reported. Oxidation with K3Fe(CN)(6) reveals a band in the near-IR with lambda(max) at 1020 nm, coupled with an increase of the iron content by almost 2-fold. Fourier transform infrared spectroscopy provided additional evidence with CN-stretching vibrations at 2095, 2025-2030, and 2047 cm(-1), assigned to a ferrocyanide adduct of the enzyme. Interestingly, the low-temperature electronic paramagnetic resonance (EPR) spectra of oxidized TpNIr reveal at least three different species indicating structural heterogeneity in the coordination environment of the active site Fe ion. Given the likely 6-coordinate geometry of the active site Fe3+ ion in the ferrocyanide adduct, we propose that the rhombic EPR species can serve as a model of a hexacoordinate form of the active site.

Ramos, JJM, Afonso CAM, Branco LC.  2003.  Glass transition relaxation and fragility in two room temperature ionic liquids. Journal of Thermal Analysis and Calorimetry. 71:659-666., Number 2 AbstractWebsite
n/a
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
n/a
Ferrer, M, Rodriguez L, Rossell O, Pina F, Lima JC, Bardia MF, Solans X.  2003.  Linear ditopic acetylide gold or mercury complexes: synthesis and photophysic studies X-ray crystal structure of PPh4[Au(C CC5H4N)(2)]. Journal of Organometallic Chemistry. 678:82-89., Number 1-2 Abstract
n/a
Garattini, E, Mendel R, Romao MJ, Wright R, Terao M.  2003.  Mammalian molybdo-flavoenzymes, an expanding family of proteins: structure, genetics, regulation, function and pathophysiology. Biochemical Journal. 372:15-32. AbstractWebsite
n/a
Moura, I, Cabrito I, Almeida G, Cunha C, Romao MJ, Moura JJG.  2003.  Molecular aspects of denitrification/nitrate dissimilation. Journal of Inorganic Biochemistry. 96:195-195., Number 1 AbstractWebsite
n/a
Roque, A, Lodeiro C, Pina F, Maestri M, Dumas S, Passaniti P, Balzani V.  2003.  Multistate/multifunctional systems. A thermodynamic, kinetic, and photochemical investigation of the 4 '-dimethylaminoflavylium compound. Journal of the American Chemical Society. 125:987-994., Number 4 AbstractWebsite
n/a
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
n/a
Ricardo, CN, Inácio JA, Gerald JA, Ortigueira MD.  2003.  New BCH-Derived Sequences for CDMA Systems. 46th IEEE - Midwest Symposium on Circuits and Systems. :1255–1258. Abstract

New BCH-derived PN-EB (pseudo-noise even balanced) sequences suitable to be used in CDMA systems are presented in this paper. It is assumed a new definition for processing gain, which better accounts for the system performance regarding the narrow band noise rejection, and it is shown how to obtain high processing gain values, namely, by using zero mean spreading signals in channels with selective noise. The new sequences have low autocorrelation levels, exist in large numbers and can provide higher processing gain with selective noise.

Carvoeiras, P, Rodrigues MJ, A.G. B, Ortigueira MD.  2003.  A Prototype software for the Diagnostic of Atrial fibrillation. XXIV Congresso Português de Cardiologia and Revista Portuguesa de Cardiologia. III Abstract
n/a
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.

Goodfellow, BJ, Nunes SG, Rusnak F, Moura I, Ascenso C, Moura JJ, Volkman BF, Markley JL.  2002.  Zinc-substituted Desulfovibrio gigas desulforedoxins: resolving subunit degeneracy with nonsymmetric pseudocontact shifts, Oct. Protein Sci. 11:2464-70., Number 10 AbstractWebsite

Desulfovibrio gigas desulforedoxin (Dx) consists of two identical peptides, each containing one [Fe-4S] center per monomer. Variants with different iron and zinc metal compositions arise when desulforedoxin is produced recombinantly from Escherichia coli. The three forms of the protein, the two homodimers [Fe(III)/Fe(III)]Dx and [Zn(II)/Zn(II)]Dx, and the heterodimer [Fe(III)/Zn(II)]Dx, can be separated by ion exchange chromatography on the basis of their charge differences. Once separated, the desulforedoxins containing iron can be reduced with added dithionite. For NMR studies, different protein samples were prepared labeled with (15)N or (15)N + (13)C. Spectral assignments were determined for [Fe(II)/Fe(II)]Dx and [Fe(II)/Zn(II)]Dx from 3D (15)N TOCSY-HSQC and NOESY-HSQC data, and compared with those reported previously for [Zn(II)/Zn(II)]Dx. Assignments for the (13)C(alpha) shifts were obtained from an HNCA experiment. Comparison of (1)H-(15)N HSQC spectra of [Zn(II)/Zn(II)]Dx, [Fe(II)/Fe(II)]Dx and [Fe(II)/Zn(II)]Dx revealed that the pseudocontact shifts in [Fe(II)/Zn(II)]Dx can be decomposed into inter- and intramonomer components, which, when summed, accurately predict the observed pseudocontact shifts observed for [Fe(II)/Fe(II)]Dx. The degree of linearity observed in the pseudocontact shifts for residues >/=8.5 A from the metal center indicates that the replacement of Fe(II) by Zn(II) produces little or no change in the structure of Dx. The results suggest a general strategy for the analysis of NMR spectra of homo-oligomeric proteins in which a paramagnetic center introduced into a single subunit is used to break the magnetic symmetry and make it possible to obtain distance constraints (both pseudocontact and NOE) between subunits.

Sola, S, Brito MA, Brites D, Moura JJG, Rodrigues CMP.  2002.  Membrane structural changes support the involvement of mitochondria in the bile salt-induced apoptosis of rat hepatocytes, Nov. Clinical Science. 103:475-485., Number 5 AbstractWebsite

The accumulation of toxic bile salts within the hepatocyte plays a key role in organ injury during liver disease. Deoxycholate (DC) and glycochenodeoxycholate (GCDC) induce apoptosis in vitro and in vivo, perhaps through direct perturbation of mitochondrial membrane structure and function. In contrast, ursodeoxycholate (UDC) and its taurine-conjugated form (TUDC) appear to be protective. We show here that hydrophobic bile salts induced apoptosis in cultured rat hepatocytes, without modulating the expression of pro-apoptotic Bax protein, and caused cytochrome c release in isolated mitochondria. Co-incubation with UDC and TUDC prevented cell death and efflux of mitochondrial factors. Using spin-labelling techniques and EPR spectroscopy analysis of isolated rat liver mitochondria, we found significant structural changes at the membrane-water surface in mitochondria exposed to hydrophobic bile salts, including modified lipid polarity and fluidity, altered protein order and increased oxidative injury. UDC, TUDC and cyclosporin A almost completely abrogated DC- and GCDC-induced membrane perturbations. We conclude that the toxicity of hydrophobic bile salts to hepatocytes is mediated by cytochrome c release, through a mechanism associated with marked direct effects on mitochondrial membrane lipid polarity and fluidity, protein order and redox status, without modulation of pro-apoptotic Bax expression. UDC and TUDC can directly suppress disruption of mitochondrial membrane structure, which may represent an important mechanism of hepatoprotection by these bile salts.

Rodrigues, CM, Sola S, Brito MA, Brites D, Moura JJ.  2002.  Bilirubin directly disrupts membrane lipid polarity and fluidity, protein order, and redox status in rat mitochondria, Mar. J Hepatol. 36:335-41., Number 3 AbstractWebsite

BACKGROUND/AIMS: Unconjugated bilirubin (UCB) impairs crucial aspects of cell function and induces apoptosis in primary cultured neurones. While mechanisms of cytotoxicity begin to unfold, mitochondria appear as potential primary targets. METHODS: We used electron paramagnetic resonance spectroscopy analysis of isolated rat mitochondria to test the hypothesis that UCB physically interacts with mitochondria to induce structural membrane perturbation, leading to increased permeability, and subsequent release of apoptotic factors. RESULTS: Our data demonstrate profound changes on mitochondrial membrane properties during incubation with UCB, including modified membrane lipid polarity and fluidity (P<0.01), as well as disrupted protein mobility (P<0.001). Consistent with increased permeability, cytochrome c was released from the intermembrane space (P<0.01), perhaps uncoupling the respiratory chain and further increasing oxidative stress (P<0.01). Both ursodeoxycholate, a mitochondrial-membrane stabilising agent, and cyclosporine A, an inhibitor of the permeability transition, almost completely abrogated UCB-induced perturbation. CONCLUSIONS: UCB directly interacts with mitochondria influencing membrane lipid and protein properties, redox status, and cytochrome c content. Thus, apoptosis induced by UCB may be mediated, at least in part, by physical perturbation of the mitochondrial membrane. These novel findings should ultimately prove useful to our evolving understanding of UCB cytotoxicity.

Rodrigues, CM, Sola S, Castro RE, Laires PA, Brites D, Moura JJ.  2002.  Perturbation of membrane dynamics in nerve cells as an early event during bilirubin-induced apoptosis, Jun. J Lipid Res. 43:885-94., Number 6 AbstractWebsite

Increased levels of unconjugated bilirubin, the end product of heme catabolism, impair crucial aspects of nerve cell function. In previous studies, we demonstrated that bilirubin toxicity may be due to cell death by apoptosis. To characterize the sequence of events leading to neurotoxicity, we exposed developing rat brain astrocytes and neurons to unconjugated bilirubin and investigated whether changes in membrane dynamic properties can mediate apoptosis. Bilirubin induced a rapid, dose-dependent increase in apoptosis, which was nevertheless preceded by impaired mitochondrial metabolism. Using spin labels and electron paramagnetic resonance spectroscopy analysis of whole cell and isolated mitochondrial membranes exposed to bilirubin, we detected major membrane perturbation. By physically interacting with cell membranes, bilirubin induced an almost immediate increase in lipid polarity sensed at a superficial level. The enhanced membrane permeability coincided with an increase in lipid fluidity and protein mobility and was associated with significant oxidative injury to membrane lipids. In conclusion, apoptosis of nerve cells induced by bilirubin is mediated by its primary effect at physically perturbing the cell membrane. Bilirubin directly interacts with membranes influencing lipid polarity and fluidity, protein order, and redox status. These data suggest that nerve cell membranes are primary targets of bilirubin toxicity.

Maximo, P, Lourenco A, Feio SS, Roseiro JC.  2002.  A new prenylisoflavone from Ulex jussiaei, JUL-AUG. ZEITSCHRIFT FUR NATURFORSCHUNG SECTION C-A JOURNAL OF BIOSCIENCES. 57:609-613., Number 7-8 Abstract
n/a
loading