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PubMed2006

Mechanism of a soluble fumarate reductase from Shewanella frigidimarina: a theoretical study.

The mechanism of a unique fumarate reductase is explored using the hybrid density functional B3LYP method. The calculations show a two-step mechanism, initiated with a hydride transfer from FAD (flavin adenine dinucleotide) to fumarate, followed by a proton shift from Arg402. The rate-limiting process is assigned to the hydride transfer, and the energetics are consistent with experimental data. It is shown that the enzyme is essential to correctly position the substrate in the active site, stabilizing its extremely anionic character.

Models, Molecular↗
PubMed2000

Comparative study of clinical efficacy and tolerance in seasonal allergic conjunctivitis management with 0.1% olopatadine hydrochloride versus 0.05% ketotifen fumarate.

OBJECTIVE: To compare the clinical efficacy and tolerance of 0.1% olopatadine hydrochloride (OHC) versus 0.05% ketotifen fumarate (KF) in the management of allergic conjunctivitis. MATERIALS AND METHODS: Eighty adult patients with a history of allergy (allergic conjunctivitis, hay fever, asthmatic bronchitis and dermatitis) that were showing allergic conjunctivitis signs and symptoms (itching, hyperemia, mucous discharge and tearing) at the time of inclusion in this study were evaluated. Patients were divided in two groups, A and B. Group A patients were treated with OHC and group B patients were treated with KF. Both groups received one drop in the affected eye every 12 hrs. The start time of this study was the first patient visit, in which the medication was instilled for the first time. Both groups of patients were evaluated 30 min, 48 hr., 7 days and 14 days later. Local tolerance of each medication was evaluated. RESULTS: Clinical improvement of the signs and symptoms of allergic conjunctivitis occurred in 42.5% to 62.5% of the patients in Group A when assessed 30 min following the first topical ocular dose of olopatadine. However, mucous discharge was not affected. Forty-eight (48) hrs. after the first instillation, improvements in 57.5% to 75% of the patients were shown in every evaluated parameter. After 7 days of treatment, positive clinical results were observed in 80% to 87.5% of the treated patients. Except for the patients that were dismissed from the study before the seventh day of treatment due to the absence of therapeutic response (4/40), all patients satisfactorily completed the therapeutic plan by the seventh day. No intolerance reactions were observed in patients of this group. In Group B patients (KF), clinical improvement of the signs and symptoms measured in the study was shown in 20.0% to 47.5% 30 min after instillation. As observed with olopatadine, no improvement in the number of patients showing mucous discharge was noted at the 30-min time point. At 48 hr. after the first instillation, 27.5% to 48% of patients showed improvement in every evaluated parameter. After 7 days of treatment, improvement was observed in 60% to 75% of patients. On Day 14, positive responses were observed in 67.5% to 75% of patients. Seventeen and one-half percent of the patients were dismissed from the study before the seventh day of treatment due to the absence of a therapeutic response. Approximately 23% of the patients had mild reactions of intolerance (stinging) which was not a cause to discontinue the treatment. CONCLUSION: Olopatadine hydrochloride controlled allergic conjunctivitis symptoms and signs more rapidly and to a greater extent than ketotifen fumarate. Fewer cases of treatment failure were noted with OHC, and no local intolerance reactions were observed, while KF triggered mild reactions (stinging) in 23% of patients.

Adult↗
PubMed2000

A forced choice comfort study of olopatadine hydrochloride 0.1% versus ketotifen fumarate 0.05%.

PURPOSE: To compare the ocular comfort of two ophthalmic anti-allergic agents: olopatadine hydrochloride 0.1% and ketotifen fumarate 0.05%. SUBJECTS AND METHODS: In a double-masked, multi-centered, randomized trial, 80 subjects were asked to make a 'forced choice' based on ocular comfort between one drop of olopatadine hydrochloride 0.1% instilled in one eye and one drop of ketotifen fumarate 0.05% instilled in the contralateral eye. At one site, the incidence of adverse reactions was also reported. RESULTS: All subjects (100%) selected olopatadine as the more comfortable formulation. One site (n = 35) reported a 49% incidence of moderate burning and a 49% incidence of mild burning after ketotifen instillation. One subject (2% of population) at this site experienced no ocular discomfort with ketotifen. There were no reports of discomfort associated with olopatadine instillation. CONCLUSION: Olopatadine is a more comfortable ophthalmic preparation than ketotifen.

Choice Behavior↗
PubMed2006

Heterologous production in Wolinella succinogenes and characterization of the quinol:fumarate reductase enzymes from Helicobacter pylori and Campylobacter jejuni.

The epsilon-proteobacteria Helicobacter pylori and Campylobacter jejuni are both human pathogens. They colonize mucosal surfaces causing severe diseases. The membrane protein complex QFR (quinol:fumarate reductase) from H. pylori has previously been established as a potential drug target, and the same is likely for the QFR from C. jejuni. In the present paper, we describe the cloning of the QFR operons from the two pathogenic bacteria H. pylori and C. jejuni and their expression in Wolinella succinogenes, a non-pathogenic -proteobacterium. To our knowledge, this is the first documentation of heterologous membrane protein production in W. succinogenes. We demonstrate that the replacement of the homologous enzyme from W. succinogenes with the heterologous enzymes yields mutants where fumarate respiration is fully functional. We have isolated and characterized the heterologous QFR enzymes. The high quality of the enzyme preparation enabled us to determine unequivocally by analytical ultracentrifugation the homodimeric state of the three detergent-solubilized heterotrimeric QFR enzymes, to accurately determine the different oxidation-reduction ('redox') midpoint potentials of the six prosthetic groups, the Michaelis constants for the quinol substrate, maximal enzymatic activities and the characterization of three different anti-helminths previously suggested to be inhibitors of the QFR enzymes from H. pylori and C. jejuni. This characterization allows, for the first time, a detailed comparison of the QFR enzymes from C. jejuni and H. pylori with that of W. succinogenes.

Campylobacter jejuni↗
PubMed1998

Interaction of a menaquinol binding site with the [3Fe-4S] cluster of Escherichia coli fumarate reductase.

We have used EPR to study the interaction between the [3Fe-4S] FR3 cluster and a menaquinol (MKH2) binding site of Escherichia coli fumarate reductase (FrdABCD). The MKH2 analog 2-n-heptyl-4-hydroxyquinoline N-oxide (HOQNO) binds to FrdABCD and elicits a significant change in the EPR lineshape of the FR3 cluster of FrdB. In a mutant of FrdABCD in which His82 of FrdC is changed to Arg, this HOQNO effect is eliminated. The HOQNO effect can also be eliminated by reaction of membranes with the imidazole-reactive reagent ethoxyformic anhydride. Potentiometric titrations indicate that neither HOQNO nor [Arg82]FrdC have a detectable effect on the midpoint potential (Em.7) of FR3. Quinol:fumarate oxidoreductase activity assays confirm that HOQNO and [Arg82]FrdC both block MKH2 oxidation by FrdABCD. Fluorescence spectroscopy was used to quantitate HOQNO binding to FrdABCD; approximately 1.30 binding sites were detected/FR3 cluster. Overall, the data support a quinol-binding model for FrdABCD in which one site has a close functional relationship with the FR3 cluster.

Amino Acid Substitution↗
PubMed2005

Experimental support for the "E pathway hypothesis" of coupled transmembrane e- and H+ transfer in dihemic quinol:fumarate reductase.

Reconciliation of apparently contradictory experimental results obtained on the quinol:fumarate reductase, a diheme-containing respiratory membrane protein complex from Wolinella succinogenes, was previously obtained by the proposal of the so-called "E pathway hypothesis." According to this hypothesis, transmembrane electron transfer via the heme groups is strictly coupled to cotransfer of protons via a transiently established pathway thought to contain the side chain of residue Glu-C180 as the most prominent component. Here we demonstrate that, after replacement of Glu-C180 with Gln or Ile by site-directed mutagenesis, the resulting mutants are unable to grow on fumarate, and the membrane-bound variant enzymes lack quinol oxidation activity. Upon solubilization, however, the purified enzymes display approximately 1/10 of the specific quinol oxidation activity of the wild-type enzyme and unchanged quinol Michaelis constants, K(m). The refined x-ray crystal structures at 2.19 A and 2.76 A resolution, respectively, rule out major structural changes to account for these experimental observations. Changes in the oxidation-reduction heme midpoint potential allow the conclusion that deprotonation of Glu-C180 in the wild-type enzyme facilitates the reoxidation of the reduced high-potential heme. Comparison of solvent isotope effects indicates that a rate-limiting proton transfer step in the wild-type enzyme is lost in the Glu-C180 --> Gln variant. The results provide experimental evidence for the validity of the E pathway hypothesis and for a crucial functional role of Glu-C180.

Cell Membrane↗
PubMed1990

Site-directed mutagenesis of conserved cysteine residues in Escherichia coli fumarate reductase: modification of the spectroscopic and electrochemical properties of the [2Fe-2S] cluster.

Site-directed mutants of Escherichia coli fumarate reductase in which each of the four N-terminal cysteine residues in the FrdB subunit, residues 57, 62, 65, and 77, was mutated individually to serine have been constructed, overexpressed, and investigated in terms of enzymatic activity as well as the EPR and redox properties of the iron-sulfur centers. In each case, the mutant contains a functional fumarate reductase in which all three of the constituent iron-sulfur clusters (i.e., center 1, [2Fe-2S]; center 2, [4Fe-4S]; center 3, [3Fe-4S]) have been assembled. The mutations affect the properties of center 1 only and demonstrate that the anomalously high redox potential of this [2Fe-2S] center is essential for optimal enzymatic activity. The results are consistent with cysteines 57, 62, 65, and 77 providing the ligands to center 1 but leave open the possibility of noncysteinyl coordination for the localized valence Fe(III) site of the reduced cluster. The implications of the results for the role of center 1 in the electron-transfer pathway and the valence localization of reduced center 1 are discussed.

Cysteine↗
PubMed2002

Mechanism of superoxide and hydrogen peroxide formation by fumarate reductase, succinate dehydrogenase, and aspartate oxidase.

Oxidative stress is created in aerobic organisms when molecular oxygen chemically oxidizes redox enzymes, forming superoxide (O2*-) and hydrogen peroxide (H2O2). Prior work identified several flavoenzymes from Escherichia coli that tend to autoxidize. Of these, fumarate reductase (Frd) is notable both for its high turnover number and for its production of substantial O2*- in addition to H2O2. We have sought to identify characteristics of Frd that predispose it to this behavior. The ability of excess succinate to block autoxidation and the inhibitory effect of lowering the flavin potential indicate that all detectable autoxidation occurs from its FAD site, rather than from iron-sulfur clusters or bound quinones. The flavin adenine dinucleotide (FAD) moiety of Frd is unusually solvent-exposed, as evidenced by its ability to bind sulfite, and this may make it more likely to react adventitiously with O2*-. The autoxidizing species is apparently fully reduced flavin rather than flavosemiquinone, since treatments that more fully reduce the enzyme do not slow its turnover number. They do, however, switch the major product from O2*- to H2O2. A similar effect is achieved by lowering the potential of the proximal [2Fe-2S] cluster. These data suggest that Frd releases O2*- into bulk solution if this cluster is available to sequester the semiquinone electron; otherwise, that electron is rapidly transferred to the nascent superoxide, and H2O2 is the product that leaves the active site. This model is supported by the behavior of "aspartate oxidase" (aspartate:fumarate oxidoreductase), an Frd homologue that lacks Fe-S clusters. Its dihydroflavin also reacts avidly with oxygen, and H2O2 is the predominant product. In contrast, succinate dehydrogenase, with high potential clusters, generates O2*- exclusively. The identities of enzyme autoxidation products are significant because O2*- and H2O2 damage cells in different ways.

Amino Acid Oxidoreductases↗
PubMed1994

Rapid purification of yeast cytoplasmic fumarate reductase by affinity chromatography on blue sepharose CL-6B.

The rapid and effective purification of soluble fumarate reductase from baker's yeast achieved by Blue Sepharose CL-6B chromatography. Cibacron Blue F3GA, the chromophore of Blue Sepharose, inhibited the activity of fumarate reductase. The enzyme bound to the column was selectively eluted by flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN) or riboflavin. The purified enzyme was essentially homogeneous as indicated by polyacrylamide gel electrophoresis under nondenaturing conditions and under denaturing conditions in sodium dodecylsulfate. By this procedure, the enzyme could be rapidly purified with high yield from yeast cells.

Chromatography, Affinity↗
PubMed2003

Crosslinking characteristics of and cell adhesion to an injectable poly(propylene fumarate-co-ethylene glycol) hydrogel using a water-soluble crosslinking system.

The crosslinking characteristics of an injectable poly(propylene fumarate-co-ethylene glycol) [P(PF-co-EG)]-based hydrogel were investigated. A water-soluble crosslinking system was used, consisting of poly(ethylene glycol) diacrylate (PEG-DA), ammonium persulfate (APS), and ascorbic acid (AA). The effects of PEG block length of the P(PF-co-EG), APS concentration, AA concentration, and PEG-DA concentration on equilibrium water content, sol fraction, onset of gelation, mechanical properties, and endothelial cell adhesion were studied. The equilibrium water content of the hydrogels ranged from 57.1 +/- 0.3 to 79.7 +/- 0.2% whereas the sol fraction ranged from 2.5 +/- 0.0 to 3.33 +/- 5.4%. The onset of gelation times varied from 1.1 +/- 0.1 to 4.3 +/- 0.2 min. For all hydrogel formulations, the tensile strength fell between 61.7 +/- 18.2 and 401.3 +/- 67.5 kPa and tensile moduli ranged from 0.4 +/- 0.0 to 3.3 +/- 0.3 MPa. Endothelial cells attached to the hydrogels in a range of 3.9 +/- 1.4 to 31.1 +/- 14.1% of cells seeded. These findings suggest that injectable poly(propylene fumarate-co-ethylene glycol) hydrogel formulations in conjunction with a novel water-soluble crosslinking system may be useful for in situ crosslinkable tissue-engineering applications.

Ammonium Sulfate↗
PubMed2001

Treatment of anemia with microencapsulated ferrous fumarate plus ascorbic acid supplied as sprinkles to complementary (weaning) foods.

BACKGROUND: Standard therapy for anemia in infants is ferrous sulfate drops administered 3 times/d. Adherence to treatment, however, is often poor. One likely reason for poor adherence is the unpleasant side effects associated with drops. OBJECTIVE: The objective was to evaluate the use of a new form of iron and a delivery system to treat anemia in infants that is likely to produce better adherence to treatment. DESIGN: Using a prospective, randomized, controlled design, we studied 557 anemic children aged 6-18 mo (hemoglobin: 70-99 g/L) in rural Ghana. One group received a daily sachet of microencapsulated ferrous fumarate (80 mg elemental Fe) in powder form plus ascorbic acid to be sprinkled onto any complementary food eaten (sprinkles group); a control group received ferrous sulfate drops 3 times/d for 2 mo (total dose: 40 mg elemental Fe). Hemoglobin and serum ferritin concentrations were measured at baseline and at the end of treatment. RESULTS: Successful treatment of anemia (hemoglobin > 100 g/L) occurred in 58% of the sprinkles group and in 56% of the drops group, with minimal side effects in both groups. Geometric mean ferritin concentrations increased significantly in each group from baseline to the end of treatment (P < 0.001). CONCLUSION: Use of ferrous sulfate drops or a single daily dose of microencapsulated ferrous fumarate sprinkles plus ascorbic acid resulted in a similar rate of successful treatment of anemia without side effects. To our knowledge, this is the first demonstration of the use of microencapsulated iron sprinkles to treat anemia. Improved ease of use may favor the use of sprinkles to deliver iron.

Anemia, Iron-Deficiency↗
PubMed1996

Randomized controlled trial of clemastine fumarate for treatment of experimental rhinovirus colds.

We used a rhinovirus challenge model to test the therapeutic efficacy of clemastine fumarate for reducing sneezing and nasal secretion in a double-blind, randomized clinical trial. Clemastine fumarate (1.34 mg) or placebo was administered at 8 A.M. and 8 P.M. for 4 days, beginning 24 hours, 36 hours, 48 hours, and 60 hours after viral challenge. Infected evaluable subjects who received clemastine (n = 75) had reduced sneeze-severity scores compared with those who received placebo (n = 75) on illness days 2 (0.3 vs. 0.5; P = .003), 3 (0.4 vs. 0.8; P = .0003), 4 (0.3 vs. 0.5; P = .025), and 5 (0.1 vs. 0.3; P = .03); sneeze counts for infected evaluable subjects (vs. counts for those who received placebo) were reduced on illness days 2 (1.5 vs. 3.1; P = .01), 3 (1.7 vs. 5.6; P = .0001), and 5 (0.7 vs. 1.9; P = .03). Infected evaluable subjects who received treatment had reduced rhinorrhea scores (compared with those who received placebo) on illness days 2 (0.7 vs. 1.0; P = .04) and 3 (0.6 vs. 0.9; P = .04) and had reduced nasal secretion weights on day 3 (3.6 g vs. 6.3 g; P = .03). Over 4 days of treatment, mean sneeze scores for infected evaluable subjects (vs. scores for those who received placebo) were reduced by 50%, mean sneeze counts by 57%, mean rhinorrhea scores by 27%, and mean nasal secretion weights by 35%. Other cold symptoms were unaffected by treatment. Treatment with clemastine was associated with an excess incidence of dry mouth (6%), dry nose (19%), and dry throat (17%).

Administration, Intranasal↗
PubMed1996

Cloning and sequencing of the gene encoding the soluble fumarate reductase from Saccharomyces cerevisiae.

A gene of the soluble fumarate reductase (FRDS) that binds FAD non-covalently was cloned by polymerase chain reaction (PCR) using degenerate oligonucleotides designed from partial amino acid sequences of highly purified enzyme. The nucleotide sequence of a 0.99-kb amplified product was found to be nearly identical to a partial sequence of an open reading frame (ORF) previously reported (EMBL database accession number S-30830). According to the sequence in the EMBL database, we cloned 1.7-kb fragment containing entire sequence of this ORF by PCR and found that this fragment contained a perfect match to the 0.99-kb sequence amplified with the degenerate primers. From these results, we concluded that this ORF is the FRDS gene. The amino acid sequences of the regions involved in the non-covalent binding of FAD and the active site, which are conserved among the flavoprotein subunits of membrane-bound fumarate reductase and succinate dehydrogenase, were found in FRDS. However, unlike the membrane-bound enzymes, FRDS did not contain the histidine residue that covalently binds the isoalloxazine ring of FAD at or near the corresponding position. FRDS showed high homology to the product of S. cerevisiae OSM1 gene which was reported to be required for growth in hypertonic media.

Amino Acid Sequence↗
PubMed1981

Partial replacement of succinate dehydrogenase function by phage- and plasmid-specified fumarate reductase in Escherichia coli.

Phages capable of transducing succinate dehydrogenase mutants (sdh) of Escherichia coli were isolated from pools of artificially constructed recombinant lambda phages using a selective casein digest medium. These phages produced characteristically dense turbid plaques, and as prophages they increased the aerobic growth efficiencies of sdh mutants on complex media but were unable to promote growth with succinate as sole carbon and energy source (an essential feature of sdh + strains). The phages were identified as fumarate reductase transducing phages (lambda frdA) by the presence of a characteristic 4.9 kilobase pairs R.HindIII fragment of bacterial DNA, the expression of a polypeptide with a relative molecular mass of 72,000 (the frdA gene product) and by comparing their transducing activities with authentic lambda frdA phages. In parallel studies a strain containing a ColE1-frd hybrid plasmid (pGS1 = pLC16.43) was characterized. Transfer of pGS1 to sdh mutants was accompanied by increased aerobic growth efficiencies on complex media and the ability to utilize succinate as sole carbon and energy source. It was concluded that fumarate reductase can replace succinate dehydrogenase but the extent of the reversal of the sdh lesion depends on frd gene dosage and the titration of the repressor which normally prevents aerobic synthesis of the reductase.

Bacteriophage lambda↗
PubMed1986

Isolation and characterization of the tubular organelles induced by fumarate reductase overproduction in Escherichia coli.

Strains of Escherichia coli amplifying the intrinsic membrane enzyme fumarate reductase accommodate the overproduced enzyme by increasing the amount of membrane material, in the form of intracellular tubular structures. These tubules have been observed in strains harbouring multicopy frd plasmids and in ampicillin hyper-resistant strains. A procedure has been developed for isolation of tubules nearly free of cytoplasmic membrane. Using protein A-gold labelling and optical diffraction of electron micrographs, a model for tubule structure is proposed. The tubules have a lower lipid/protein ratio than the cytoplasmic membrane, with the enzyme accounting for greater than 90% of the protein in the tubules. Both cytoplasmic membranes and tubules from amplified strains are enriched in cardiolipin and have a more fluid fatty acid composition than wild-type strains. Mutants defective in cardiolipin synthesis produce tubules in response to excess fumarate reductase, but these tubules have an altered appearance, indicating that lipid-protein interactions may be important for tubule assembly.

Bacterial Proteins↗
PubMed2000

Triethylammonium hydrogen fumarate.

In crystals of the title compound, the hydrogen fumarate anions form one-dimensional chains through an O-H.O hydrogen bonding along the c and (a+b)/2 directions. There are three sites of the hydrogen fumarate, two of which have an inversion centre.

Journal Article↗
PubMed2004

The 2:1 adducts of (benzoylmethylene)triphenylphosphorane with fumaric and terephthalic acids.

Co-crystals of the ylide (benzoylmethylene)triphenylphosphorane (BPPY) with either fumaric acid, viz. (benzoylmethylene)triphenylphosphorane-fumaric acid (2/1), C(26)H(21)OP.0.5C(4)H(4)O(4), or terephthalic acid, viz. (benzoylmethylene)triphenylphosphorane-terephthalic acid (2/1), C(26)H(21)OP.0.5C(8)H(6)O(4), have a stoichiometric ratio of 2:1 between the ylide and the corresponding dicarboxylic acid. In both adducts, the acid component lies across a centre of inversion. In neither case is the ylide protonated by the organic acid; instead the H atoms of the non-ionized dicarboxylic acid molecules participate in the formation of strong O-H...O hydrogen bonds with the benzoyl O atom of the ylide species. These structures are the first reported examples of co-crystals containing non-protonated BPPY.

Journal Article↗