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M Teixeira

Publications and source records attributed to M Teixeira.

At least 73 records · Page 4Linked to original sources
PubMed1999

Evidence for apical K conductance and Na-K-2Cl cotransport in the endolymphatic sac of guinea pig.

The transepithelial potential in the endolymphatic sac (ESP) was recorded up to 60 min after apical injection of ouabain, bumetanide, quinine, barium, tetraethylammonium, and 4-aminopyridine. After control injection, ESP decreased by 74% and completely recovered at 30 min. After ouabain, barium, or quinine injection, the ESP time course was similar to that in the control group. After bumetanide, tetraethylammonium, or 4-aminopyridine injection, complete recovery was only observed at 60 min. These results suggest that apical K+ conductance and Na-K-2Cl cotransporter could be involved in the genesis of ESP.

Animals↗
PubMed1999

Desulfovibrio gigas neelaredoxin. A novel superoxide dismutase integrated in a putative oxygen sensory operon of an anaerobe.

Neelaredoxin, a small non-heme blue iron protein from the sulfate-reducing bacterium Desulfovibrio gigas [Chen, L., Sharma, P., LeGall, J., Mariano, A.M., Teixeira M. and Xavier, A.V. (1994) Eur. J. Biochem. 226, 613-618] is shown to be encoded by a polycistronic unit which contains two additional open reading frames (ORF-1 and ORF-2) coding for chemotaxis-like proteins. ORF-1 has domains highly homologous with those structurally and functionally important in methyl-accepting chemotaxis proteins, including two putative transmembrane helices, potential methylation sites and the interaction domain with CheW proteins. Interestingly, ORF-2 encodes a protein having homologies with CheW proteins. Neelaredoxin is also shown to have significant superoxide dismutase activity (1200 U. mg-1), making it a novel type of iron superoxide dismutase. Analysis of genomic data shows that neelaredoxin-like putative polypeptides are present in strict anaerobic archaea, suggesting that this is a primordial superoxide dismutase. The three proteins encoded in this operon may be involved in the oxygen-sensing mechanisms of this anaerobic bacterium, indicating a possible transcriptional mechanism to sense and respond to potential stress agents.

Amino Acid Sequence↗
PubMed1999

The superoxide dismutase activity of desulfoferrodoxin from Desulfovibrio desulfuricans ATCC 27774.

Desulfoferrodoxin (Dfx), a small iron protein containing two mononuclear iron centres (designated centre I and II), was shown to complement superoxide dismutase (SOD) deficient mutants of Escherichia coli [Pianzzola, M.J., Soubes M. & Touati, D. (1996) J. Bacteriol. 178, 6736-6742]. Furthermore, neelaredoxin, a protein from Desulfovibrio gigas containing an iron site similar to centre II of Dfx, was recently shown to have a significant SOD activity [Silva, G., Oliveira, S., Gomes, C.M., Pacheco, I., Liu, M.Y., Xavier, A.V., Teixeira, M., Le Gall, J. & Rodrigues-Pousada, C. (1999) Eur. J. Biochem. 259, 235-243]. Thus, the SOD activity of Dfx isolated from the sulphate-reducing bacterium Desulfovibrio desulfuricans ATCC 27774 was studied. The protein exhibits a SOD activity of 70 U x mg-1, which increases approximately 2.5-fold upon incubation with cyanide. Cyanide binds specifically to Dfx centre II, yielding a low-spin iron species with g-values at 2.27 (g perpendicular) and 1.96 (g parallel). Upon reaction of fully oxidized Dfx with the superoxide generating system xanthine/xanthine oxidase, Dfx centres I and II become partially reduced, suggesting that Dfx operates by a redox cycling mechanism, similar to those proposed for other SODs. Evidence for another SOD in D. desulfuricans is also presented - this enzyme is inhibited by cyanide, and N-terminal sequence data strongly indicates that it is an analogue to Cu,Zn-SODs isolated from other sources. This is the first indication that a Cu-containing protein may be present in a sulphate-reducing bacterium.

Amino Acid Sequence↗
PubMed1999

In vivo study of the electrochemical composition of luminal fluid in the guinea pig endolymphatic sac.

The aim of this study was to investigate the ionic composition (sodium, potassium) of the luminal fluid in the endolymphatic sac and to correlate it with the transepithelial potential. Experiments were performed in guinea pigs using either an intradural posterior fossa approach or a translabyrinthine approach. The endolymphatic sac transepithelial potential (ESP) was measured and the luminal fluid was sampled. The sodium, potassium and protein concentrations were determined. The results were: i) the luminal fluid in the endolymphatic sac differs in composition from perilymph, on the one hand, and from both cochlear and vestibular endolymph, on the other hand, indicating that the endolymphatic sac maintains chemical (sodium, potassium) and electrical (ESP) gradients; ii) the calculated osmolarity (Na + K) x 2 was about 230 mosm/l; iii) no correlation was observed between sodium and potassium concentrations; iv) large interindividual variations exist from one animal to another, suggesting physiological variations in the functional status of the endolymphatic sac. In conclusion, the variation in composition of the endolymphatic sac luminal fluid reflected variations in ion transport by the epithelium and thus a possible adaptation of the ion transport to different physiopathological conditions.

Animals↗
PubMed1999

[Angioplasty with stenting in single vessel disease: non invasive methods for detecting restenosis].

OBJECTIVE: To compare the value of the myocardial perfusion imaging with 99Tc sestamibi (MIBI) with clinical data and stress EKG (SEKG) variables, in the detection of angiographic restenosis (AR: lesion > 50%), in a group of patients (pts) with single vessel disease (angiographic lesion above 70% in one epicardial artery), submitted to coronary angioplasty (PTCA) with stenting. POPULATION AND METHODS: Fifty-nine pts, followed prospectively, (49 males and 10 females aged 57 +/- 10) were submitted to 61 angioplasties, with dilatation of 59 vessels, and with stenting in 63 (1.07 stent/vessel). Clinical evaluation was performed in the first, third and sixth month, SEKG with MIBI in the fourth month and recatheterization for angiographic control in the sixth month. The pts were divided in two groups: R-positive angiographic restenosis (AR)--14 pts: NR--without AR--45 pts; the angiographic restenosis rate was 23.7%. The patients' history, cause of admission, procedure characteristics, medication at discharge, clinical events during follow-up, variables of stress EKG associated with myocardial perfusion and angiographic control were analyzed. RESULTS: The cause of admission was the same in both groups (MI in R group: 28.6%; NR: 46.7%; p = ns). There was no difference in the discharge medication. The R group was more symptomatic (Angina: R = 50.0% vs NR = 11.1%; p < 0.001 clinical restenosis rate = 11.8%), and had more revascularization procedures (PTCA: R = 57.1% vs NR = 2.8%; p < 0.001/Bypass surgery: R = 14.3% vs NR = 0%; p = 0.01). This group had abnormal stress EKG more frequently (42.9 vs 20.0%, p = ns) and ischemia in the myocardial perfusion scintigraphy (57.1 vs 6.7% p < 0.001). [table: see text] CONCLUSION: The clinical and diagnostic tests evaluated in this study showed a limited sensitivity in the detection of angiographic restenosis in a group of patients with single vessel disease submitted to coronary angioplasty and stenting. Myocardial scintigraphy was the best method for the detection of angiographic restenosis, showing a high specificity and a reasonable sensitivity.

Angioplasty↗
PubMed1998

Ambineela, an unusual blue protein isolated from the archaeon Acidianus ambivalens.

A novel blue protein, named ambineela, was isolated from the soluble extract of the thermoacidophilic archaeon Acidianus ambivalens. In solution, the purified protein is a monomer with 50 kDa and has a basic character (pI approximately 8.7). The electronic spectrum shows two bands, centred at 395 and 625 nm (A625/A395 = 0.7). The protein does not contain any transition metal; its blue colour is due to an unidentified non-fluorescent cofactor, covalently bound to it. Ambineela N-terminal sequence exhibits a consensus ADP-binding region, suggesting that its unknown cofactor may comprise this molecule or an analogue.

Adenosine Diphosphate↗
PubMed1998

Evidence for a novel type of iron cluster in the respiratory chain of the archaeon Sulfolobus metallicus.

A new type of metal centre was detected in the membranes of the thermoacidophilic archaeon Sulfolobus metallicus. This centre has an S = 1/2 ground state in the oxidised form, yielding an axial EPR signal with g values at 2.035 (g(parallel)) and 1.97 (g(perpendicular)), optimally detected at 4.6-10 K; in the reduced form it is EPR silent (even spin). These magnetic properties point to a spin-coupled iron cluster, with a minimum of two iron ions. The centre has a high reduction potential of +350 mV, at pH 6.5. The physiological role of this novel centre was probed through a general characterisation of S. metallicus respiratory chain: this archaeon contains NADH and succinate dehydrogenase activities, and cytochromes b562, a586 and a600 on the oxygen reductase system. Since it is reduced in the presence of succinate, and taking into account its high reduction potential, this centre is proposed to be a functional analogue of the Rieske centres.

Animals↗
PubMed1998

Characterisation of a new rubredoxin isolated from Desulfovibrio desulfuricans 27774: definition of a new family of rubredoxins.

A new rubredoxin from the sulphate-reducing bacterium Desulfovibrio desulfuricans ATCC 27774, grown with nitrate as terminal electron acceptor, was isolated and characterised. The protein is an 8.5 kDa monomer containing one iron atom per molecule, with a reduction potential of 25 +/- 5 mV at pH 7.6. Like the recombinant Rdl protein from D. vulgaris, expressed in Escherichia coli [Lumpio, H.L., Shenvi, N.V., Garg, R.P., Summers, A.O. and Kurtz, D.M., J. Bacteriol. 179 (1997) 4607-4615], it contains an unusual spacing of four amino acids between the first two of the iron coordinating cysteinyl residues. This difference is reflected in the structure of the iron centre, as observed by visible and EPR spectroscopies. All together, these features make these proteins the first members of a new family of rubredoxins.

Amino Acid Sequence↗
PubMed1998

The NADH oxidase from the thermoacidophilic archaea Acidianus ambivalens: isolation and physicochemical characterisation.

A flavoprotein with NADH oxidising activity (NADH: acceptor oxidoreductase) was isolated from the soluble fraction of the thermoacidophilic archaea Acidianus ambivalens. The protein is a monomer with a molecular mass of 70 kDa and contains FAD as single cofactor. Its activity as NADH:O2 oxidoreductase is FAD, but not FMN, dependent and yields hydrogen peroxide as the reaction product. The activity decreases with pH in the range 4.5 to 9.8, and increases with the temperature, as tested from 30 degrees to 60 degrees C. As elicited by EPR, the purified enzyme also acts as an NADH:ferredoxin oxidoreductase. These features are discussed in light of the possible involvement of this protein in the metabolism of this archaea.

Flavoproteins↗
PubMed1998

Taurine entry into perilymph of the guinea pig.

Taurine is a beta-aminosulfonic acid and is a ubiquitous amino acid whose role in the cochlea is not well established. In this study, its entry from blood into perilymph was investigated in the guinea pig as animal model. The penetration rate of [3H]taurine (molecular weight 125) into the perilymph of the scala vestibuli was measured 1 and 2 h after the intravenous infusion of [3H]taurine in nephrectomized animals. Results showed a rate of penetration in perilymph related to plasma at 36 +/- 4.7% (n = 5) after 1 h and 43 +/- 5.6% (n = 5) after 2 h. Compared to the penetration rate of urea (molecular weight 60) and mannitol (molecular weight 186) reported previously in rats, a passive entry of taurine into perilymph through the blood-perilymph barrier is suggested.

Animals↗
PubMed1998

The effects of perilymphatic tonicity on endolymph composition and synaptic activity at the frog semicircular canal.

The effects of changes in perilymphatic tonicity on the semicircular canal were investigated by combining the measurements of transepithelial potential and endolymphatic ionic composition in the isolated frog posterior canal with the electrophysiological assessment of synaptic activity and sensory spike firing at the posterior canal in the isolated intact labyrinth. In the isolated posterior canal, the endolymph was replaced by an endolymph-like solution of known composition, in the presence of basolateral perilymph-like solutions of normal (230 mosmol/kg), reduced (105 mosmol/kg, low NaCl) or increased osmolality (550 mosmol/kg, Na-Gluconate added). Altered perilymphatic tonicity did not produce significant changes in endolymphatic ionic concentrations during up to 5 min. In the presence of hypotonic perilymph, decreased osmolality, K and Cl concentrations were observed at 10 min. In the presence of hypertonic perilymph, the endolymphatic osmolality began to increase at 5 min and by 10 min Na concentration had also significantly increased. On decreasing the tonicity of the external solution an immediate decline was observed in transepithelial potential, whereas hypertonicity produced the opposite effect. In the intact frog labyrinth, mEPSPs and spike potentials were recorded from single fibers of the posterior nerve in normal Ringer's (240 mosmol/kg) as well as in solutions with modified tonicity. Hypotonic solutions consistently decreased and hypertonic solutions consistently increased mEPSP and spike frequencies, independent of the species whose concentration was altered. These effects ensued within 1-2 min after the start of perfusion with the test solutions. In particular, when the tonicity was changed by varying Na concentration the mean mEPSP rate was directly related to osmolality. Size histograms of synaptic potentials were well described by single log-normal distribution functions under all experimental conditions. Hypotonic solutions (105 mosmol/kg) markedly shifted the histograms to the left. Hypertonic solutions (380-550 mosmol/kg, NaCl or Na-Gluconate added) shifted the histograms to the right. Hypertonic solutions obtained by adding sucrose to normal Ringer's solution (final osmolality 550 mosmol/kg) increased mEPSP and spike rates, but did not display appreciable effects on mEPSP size. All effects on spike discharge and on mEPSP rate and size were rapidly reversible. In Ca-free, 10 mM EGTA, Ringer's solution, the sensory discharge was completely abolished and did not recover on making the solution hypertonic. These results indicate that perilymphatic solutions with altered tonicity produce small and slowly ensuing changes in the transepithelial parameters which may indirectly affect the sensory discharge rate, whereas relevant, early and reversible effects occur at the cytoneural junction. In particular, the modulation of mEPSP amplitude appears to be postsynaptic; the presynaptic effect on mEPSP rate of occurrence is presumably linked to local calcium levels, in agreement with previous results indicating that calcium inflow is required to sustain basal transmitter release in this preparation.

Action Potentials↗
PubMed1998

Uric acid in chronic heart failure: a marker of chronic inflammation.

BACKGROUND: Chronic heart failure is associated with hyperuricaemia and elevations in circulating markers of inflammation. Activation of xanthine oxidase, through free radical release, causes leukocyte and endothelial cell activation. Associations could therefore be expected between serum uric acid level, as a marker of increased xanthine oxidase activity, and markers of inflammation. We have explored these associations in patients with chronic heart failure, taking into account the hyperuricaemic effects of diuretic therapy and insulin resistance. METHODS AND RESULTS: Circulating uric acid and markers of inflammation were measured in 39 male patients with chronic heart failure and 16 healthy controls. All patients underwent a metabolic assessment, which provided a measure of insulin sensitivity (intravenous glucose tolerance tests and minimal modelling analysis). Compared to controls, patients with chronic heart failure had significantly higher levels of circulating uric acid, interleukin-6, soluble tumour necrosis factor receptor (sTNFR)-1, soluble intercellular adhesion molecule-1 (ICAM-1, all P<0.001), E-selectin and sTNFR2 (both P<0.05). In patients with chronic heart failure, serum uric acid concentrations correlated with circulating levels of sTNFR1 (r=0.74), interleukin-6 (r=0.66), sTNFR2 (r=0.63), TNFa (r=0.60) (all P<0.001), and ICAM-1 (r=0.41, P<0.01). In stepwise regression analyses, serum uric acid emerged as the strongest predictor of ICAM-1, interleukin-6, TNF, sTNFR1 and sTNFR2, independent of diuretic dose, age, body mass index, alcohol intake, serum creatinine, plasma insulin and glucose, and insulin sensitivity. CONCLUSIONS: Serum uric acid is strongly related to circulating markers of inflammation in patients with chronic heart failure. This is consistent with a role for increased xanthine oxidase activity in the inflammatory response in patients with chronic heart failure.

Cardiomyopathy, Dilated↗
PubMed1997

Functional properties of the quinol oxidase from Acidianus ambivalens and the possible catalytic role of its electron donor--studies on the membrane-integrated and purified enzyme.

The aa3 quinol oxidase has been purified from the thermoacidophilic archaea Acidianus ambivalens as a three-redox-centers enzyme. The functional properties of this oxidase both as purified and in its most integral form (i.e. in native membranes and in intact cells) were investigated by stopped-flow spectrophotometry. The results suggest that the enzyme interacts in vivo with a redox-active molecule, which favours the electron entry via heme a and provides the fourth electron demanded for catalysis. We observe that the purified enzyme has two hemes with apparent redox potentials 215 +/- 20 mV and 415 +/- 20 mV at pH 5.4, showing redox-Bohr effect, and a heme a3-CuB center with an affinity for carbon monoxide (Ka = 5.7 x 10(4) M(-1) at 35 degrees C) much lower than that reported for the mammalian enzyme (Ka = 4 x 10(6) M(-1) at 20 degrees C). The reduction by dithionite is fast and monophasic when the quinol oxidase is in the native membranes, whereas it is slow and biphasic in the purified enzyme (with heme a3 being reduced faster than heme a). The oxygen reaction of the reduced purified enzyme is fast (few milliseconds), but yields an intermediate (likely ferryl) clearly different from the fully oxidized enzyme. In contrast, the same reaction performed in intact cells leads to the fully oxidized enzyme. We postulate that caldariella quinol, the physiological electron donor, is in vivo tightly bound to the enzyme, providing the fourth redox active center lacking in the purified enzyme.

Dithionite↗
PubMed1997

Characterization of the [NiFe] hydrogenase from the sulfate reducer Desulfovibrio vulgaris Hildenborough.

The [NiFe] hydrogenase from Desulfovibrio vulgaris Hildenborough was isolated from the cytoplasmic membranes and characterized by EPR spectroscopy. It has a total molecular mass of 98.7 kDa (subunits of 66.4 and 32.3 kDa), and contains 1 nickel and 12 Fe atoms per heterodimer. The catalytic activities for hydrogen consumption and production were determined to be 174 and 89 mumol H2.min-1.mg-1, respectively. As isolated, under aerobic conditions, this hydrogenase exhibits EPR signals characteristic of the nickel centers in [NiFe] hydrogenases (Ni-A signal at gx,y,z = 2.32, 2.23 and approximately 2.0 and Ni-B signal at gx,y,z = 2.33, 2.16 and approximately 2.0) as well as an intense quasi-isotropic signal centered at g = 2.02 due to the oxidized [3Fe-4S] center. The redox profile under hydrogen atmosphere is remarkably similar to that of other [NiFe] hydrogenases. The signals observed for the oxidized state disappear, first being substituted by the Ni-C type signal (gx,y,z = 2.19, 2.14, approximately 2.01), which upon long incubation under hydrogen yields the split Ni-C signal due to interaction with the reduced [4Fe-4S] centers.

Amino Acid Sequence↗
PubMed1997

The iron-sulfur centers of the pyruvate:ferredoxin oxidoreductase from Methanosarcina barkeri (Fusaro).

The iron-sulfur clusters of a pyruvate:ferredoxin oxidoreductase isolated from a methanogenic archaeon, Methanosarcina barkeri (Fusaro), have been unambiguously identified for the first time. In agreement with the estimated iron and sulfur contents (Bock and Schonheit, Eur. J. Biochem., 237 (1996) 35-44), the enzyme is shown to contain three [4Fe-4S](2+/1+) clusters, which in the reduced state give a complex EPR spectrum resulting from three distinct centres, magnetically interacting. The catalytic cycle of the enzyme was studied by visible and EPR spectroscopies. A thiamine diphosphate based radical is also an intermediate in the M. barkeri enzyme catalytic cycle. However, under anaerobic conditions, the enzyme or Clostridium pasteurianum ferredoxin iron-sulfur clusters are reduced only in the presence of both substrates, pyruvate and coenzyme A.

Anaerobiosis↗
PubMed1997

Studies on the redox centers of the terminal oxidase from Desulfovibrio gigas and evidence for its interaction with rubredoxin.

Rubredoxin-oxygen oxidoreductase (ROO) is the final component of a soluble electron transfer chain that couples NADH oxidation to oxygen consumption in the anaerobic sulfate reducer Desulfovibrio gigas. It is an 86-kDa homodimeric flavohemeprotein containing two FAD molecules, one mesoheme IX, and one Fe-uroporphyrin I per monomer, capable of fully reducing oxygen to water. EPR studies on the native enzyme reveal two components with g values at approximately 2.46, 2.29, and 1.89, which are assigned to low spin hemes and are similar to the EPR features of P-450 hemes, suggesting that ROO hemes have a cysteinyl axial ligation. At pH 7.6, the flavin redox transitions occur at 0 +/- 15 mV for the quinone/semiquinone couple and at -130 +/- 15 mV for the semiquinone/hydroquinone couple; the hemes reduction potential is -350 +/- 15 mV. Spectroscopic studies provided unequivocal evidence that the flavins are the electron acceptor centers from rubredoxin, and that their reduction proceed through an anionic semiquinone radical. The reaction with oxygen occurs in the flavin moiety. These data are strongly corroborated by the finding that rubredoxin and ROO are located in the same polycistronic unit of D. gigas genome. For the first time, a clear role for a rubredoxin in a sulfate-reducing bacterium is presented.

Amino Acid Sequence↗
PubMed1997

Multiheme cytochromes from the sulfur-reducing bacterium Desulfuromonas acetoxidans.

Two new multiheme cytochromes were isolated from the anaerobic sulfur reducing bacterium Desulfuromonas acetoxidans. They have monomeric molecular masses of 50 and 65 kDa and contain six and eight hemes, respectively. Visible and EPR spectroscopies, in the as-isolated (oxidised) cytochromes, show the presence of only low-spin hemes in the 50-kDa cytochrome, and of high-spin and low-spin hemes in the 65-kDa cytochrome. The EPR spectra of the native 65-kDa cytochrome indicate multiple heme-heme interactions, including integer-spin systems as judged by parallel-mode EPR. The 50-kDa cytochrome has a complex redox pattern, as shown by EPR redox titrations, and contains one heme with unusual characteristics. Both cytochromes cover an extremely wide range of reduction potentials, which go from +100 mV to -375 mV for the 50-kDa cytochrome, and +185 mV to -235 mV for the 65-kDa cytochrome. The two cytochromes were tested for hydroxylamine oxidoreductase activity and polysulfide reductase activity, but neither displayed any activity. In contrast, it was found for the first time that the previously characterised cytochrome c551.5, from the same bacterium is very active in the reduction of polysulfide, which suggests that it acts as a terminal reductase in D. acetoxidans.

Amino Acid Sequence↗