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Biochimica Et Biophysica Acta Jul 2001We measured the temperature dependence of oxygen evolution in thylakoids from tobacco using mass spectrometry and high resolution polarography. We determined the initial...
We measured the temperature dependence of oxygen evolution in thylakoids from tobacco using mass spectrometry and high resolution polarography. We determined the initial S-state distribution and the efficiency of the transition between these states including the probability of the O(2) yield through a fast mode. We observed discontinuous changes of the parameters at the temperatures 11 degrees C, 15 degrees C and 21 degrees C. Due to the mass spectroscopy data we think that the irregularity observed at 11 degrees C is due to conformational changes within the water catalytic site. We show that the different contributions of the slow and fast modes of oxygen evolution and of the water molecule exchange are correlated and that their behavior can be explained in terms of the H(2)O accessibility to the water splitting enzyme.
Topics: Mass Spectrometry; Models, Chemical; Oxidation-Reduction; Oxygen; Oxygen Isotopes; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Plants, Toxic; Polarography; Temperature; Thylakoids; Nicotiana; Water
PubMed: 11418096
DOI: 10.1016/s0005-2728(01)00182-7 -
Indian Journal of Dental Research :... 2012Teeth and restorations are subjected continuously to degradation in hostile physical and chemical environments, resulting in corrosion. Component of liquid or solid is...
CONTEXT
Teeth and restorations are subjected continuously to degradation in hostile physical and chemical environments, resulting in corrosion. Component of liquid or solid is an important factor influencing the corrosion of metallic appliances placed in the oral cavity.
AIMS
To study in vitro corrosion of titanium wires immersed in solutions of toothpaste and chocolate in artificial saliva.
MATERIALS AND METHODS
Immersion test and electrochemical studies using different parameters, including corrosion potential (E corr ), cathodic Tafel constant (βc), anodic Tafel constant (βa), corrosion current (I corr ), polarization resistance (R p ), and corrosion rate of titanium wires, were done in solutions of artificial saliva containing Colgate™ toothpaste and Amul™ chocolate. Photomicrographs were also taken.
RESULTS
The results showed degradation of titanium wires by electrochemical attack when they were placed in the hostile electrolytic environments provided in the experiments. Surface analysis of titanium wires showed pitting and localized attacks on the surface. Pitting corrosion was found in the titanium wires.
Topics: Cacao; Corrosion; Dental Alloys; Electrochemical Techniques; Electrolysis; Humans; Immersion; Materials Testing; Photomicrography; Polarography; Potentiometry; Saliva, Artificial; Surface Properties; Titanium; Toothpastes
PubMed: 23257481
DOI: 10.4103/0970-9290.104953 -
The Journal of Biological Chemistry Dec 2000Leber's hereditary optic neuropathy (LHON) is a form of blindness caused by mitochondrial DNA (mtDNA) mutations in complex I genes. We report an extensive biochemical...
Leber's hereditary optic neuropathy (LHON) is a form of blindness caused by mitochondrial DNA (mtDNA) mutations in complex I genes. We report an extensive biochemical analysis of the mitochondrial defects in lymphoblasts and transmitochondrial cybrids harboring the three most common LHON mutations: 3460A, 11778A, and 14484C. Respiration studies revealed that the 3460A mutation reduced the maximal respiration rate 20-28%, the 11778A mutation 30-36%, and the 14484C mutation 10-15%. The respiration defects of the 3460A and 11778A mutations transferred in cybrid experiments linking these defects to the mtDNA. Complex I enzymatic assays revealed that the 3460A mutation resulted in a 79% reduction in specific activity and the 11778A mutation resulted in a 20% reduction, while the 14484C mutation did not affect the complex I activity. The enzyme defect of the 3460A mutation transferred with the mtDNA in cybrids. Overall, these data support the conclusion that the 3460A and 11778A mutants result in complex I defects and that the 14484C mutation causes a much milder biochemical defect. These studies represent the first direct comparison of oxidative phosphorylation defects among all of the primary LHON mtDNA mutations, thus permitting insight into the underlying pathophysiological mechanism of the disease.
Topics: Cell Line; DNA, Mitochondrial; Female; Humans; Lymphocytes; Male; Mutation; Optic Atrophies, Hereditary; Polarography
PubMed: 10976107
DOI: 10.1074/jbc.M006476200 -
The Biochemical Journal Feb 1994In newborn-pig hepatocytes, the rate of oleate oxidation is extremely low, despite a very low malonyl-CoA concentration. By contrast, the sensitivity of carnitine...
In newborn-pig hepatocytes, the rate of oleate oxidation is extremely low, despite a very low malonyl-CoA concentration. By contrast, the sensitivity of carnitine palmitoyltransferase (CPT) I to malonyl-CoA inhibition is high, as suggested by the very low concentration of malonyl-CoA required for 50% inhibition of CPT I (IC50). The rates of oleate oxidation and ketogenesis are respectively 70 and 80% lower in mitochondria isolated from newborn-pig liver than from starved-adult-rat liver mitochondria. Using polarographic measurements, we showed that the oxidation of oleoyl-CoA and palmitoyl-L-carnitine is very low when the acetyl-CoA produced is channelled into the hydroxymethylglutaryl-CoA (HMG-CoA) pathway by addition of malonate. In contrast, the oxidation of the same substrates is high when the acetyl-CoA produced is directed towards the citric acid cycle by addition of malate. We demonstrate that the limitation of ketogenesis in newborn-pig liver is due to a very low amount and activity of mitochondrial HMG-CoA synthase as compared with rat liver mitochondria, and suggest that this could promote the accumulation of acetyl-CoA and/or beta-oxidation products that in turn would decrease the overall rate of fatty acid oxidation in newborn- and adult-pig livers.
Topics: Animals; Animals, Newborn; Hydroxymethylglutaryl-CoA Synthase; Ketone Bodies; Mitochondria, Liver; Oleic Acid; Oleic Acids; Oxidation-Reduction; Polarography; Rats; Swine
PubMed: 7907471
DOI: 10.1042/bj2980207 -
Fertility and Sterility May 1973
Topics: Body Fluids; Calcium; Chlorides; Electric Conductivity; Female; Humans; Male; Neuraminidase; Ovarian Follicle; Polarography; Sperm Capacitation; Spermatozoa
PubMed: 4735422
DOI: 10.1016/s0015-0282(16)39672-8 -
Analytical Sciences : the International... Apr 2002Uranium(VI) is adsorbed as a uranium trifluoroethylxanthate (TFEX)-cetyltrimethylammonium (CTMA) ion-pair complex on microcrystalline naphthalene quantitatively in the...
Differential pulse polarographic determination of uranium(VI) in complex materials after adsorption of its trifluoroethylxanthate cetyltrimethylammonium ion-associated complex on naphthalene adsorbent.
Uranium(VI) is adsorbed as a uranium trifluoroethylxanthate (TFEX)-cetyltrimethylammonium (CTMA) ion-pair complex on microcrystalline naphthalene quantitatively in the pH range 4.2 - 7.0. Without cetyltrimethylammonium as the counter ion, the adsorption is hardly 70%. The metal has been desorbed with HCI and determined with a differential pulse polarograph. Uranium can alternatively be quantitatively adsorbed on TFEX-CTMA-naphthalene adsorbent packed in a column at a flow rate of 1 - 5 ml/min and determined similarly. A well-defined peak has been obtained in this medium at -0.20 V versus a saturated calomel electrode. Cyclic voltammetry, differential pulse polarography and D.C. polarography studies indicate that uranium has been reduced irreversibly under these conditions. The detection limit is 0.30 microg/ml at the minimum instrumental settings (signal-to-noise ratio of 2) (with a preconcentration factor of 10, the detection limit would be 30 ng/ml for uranium when the volume in the cell is 15 ml). However if the volume in the cell is 5 ml, it would have been 10 ng/ml with a preconcentration factor of 30. Linearity is maintained in a concentration range of 0.5 - 19.0 microg/ml (2.1 - 79.83 x 10(-9) M) with a correlation factor of 0.9994 and a relative standard deviation of +/-1.1% (in this case 7.5 microg may be concentrated from 150 ml of the aqueous sample where its concentration is as low as 50 ng/ml). Various parameters, such as the effect of the pH, volume of the aqueous phase, flow rate and the interference of a large number of metal ions and anions on the determination of uranium, have been studied in detail to optimize the conditions for its trace determination in various complex materials, like alloys, coal fly ash, biological, synthetic, and waste-water samples.
Topics: Adsorption; Alloys; Carbon; Cations; Cetrimonium Compounds; Chlorella; Coal; Coal Ash; Hair; Humans; Hydrocarbons, Fluorinated; Hydrogen-Ion Concentration; Industrial Waste; Ions; Naphthalenes; Particulate Matter; Plant Leaves; Polarography; Tea; Uranium; Water
PubMed: 11999517
DOI: 10.2116/analsci.18.427 -
Experientia Nov 1980
Topics: Animals; Brain; Catecholamines; DNA; Electric Stimulation; Electrodes; Electrophysiology; NAD; Nitrogenase; Oxidation-Reduction; Polarography; Potentiometry; RNA
PubMed: 6161027
DOI: 10.1007/BF01969579 -
The Journal of Membrane Biology Mar 2012HCO₃⁻ translocation across the plasma membrane via the electrogenic Na/HCO₃⁻ cotransporter NBCe1 plays an important role in intracellular pH regulation and...
HCO₃⁻ translocation across the plasma membrane via the electrogenic Na/HCO₃⁻ cotransporter NBCe1 plays an important role in intracellular pH regulation and transepithelial HCO₃⁻ transport. However, the structural determinants of transporter function remain largely unknown. A previous study showed that the putative fourth extracellular loop (EL4) plays an essential role in determining the electrogenicity of NBCe1. In the present study, we generated eight new chimeras of human NBCe1-A and NBCn1-A. All possess the putative NBCe1 EL4 and are electrogenic. Chimera O, in which the putative sixth transmembrane segment (TM6) and EL5 through the C terminus (Ct) of NBCe1 was replaced by corresponding NBCn1 sequence, produces the smallest hyperpolarization (1-2 mV) when CO₂/HCO₃⁻ is added to the extracellular solution. Biotinylation experiments show that O has a very low abundance at the plasma membrane. However, chimeras in which we simultaneously replaced the putative TM6 and smaller subdomains of the EL5-Ct region for the NBCn1 sequence were strongly electrogenic except for chimera T, in which we replaced TM6 and TM12 of NBCe1 with the corresponding regions of NBCn1. T exhibited greatly reduced transporter surface expression compared to wild-type NBCe1-A, while retaining at least some electrogenic character. We hypothesize that putative TM6 and TM12 are part of a functional unit and that if the two TMs are replaced by those of the same transporter type, high surface expression would require that the surrounding TMs are also from the same transporter type.
Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Biological Transport; Cell Membrane; Humans; Hydrogen-Ion Concentration; Oocytes; Polarography; Sodium-Bicarbonate Symporters; Xenopus laevis
PubMed: 22383045
DOI: 10.1007/s00232-012-9421-y -
Applied and Environmental Microbiology Sep 2014Gordonia polyisoprenivorans strain VH2, a potent rubber-degrading actinomycete, harbors two latex clearing proteins (Lcps), which are known to be essential for the...
Gordonia polyisoprenivorans strain VH2, a potent rubber-degrading actinomycete, harbors two latex clearing proteins (Lcps), which are known to be essential for the microbial degradation of rubber. However, biochemical information on the exact role of this protein in the degradation of polyisoprene was lacking. In this study, the gene encoding Lcp1VH2 was heterologously expressed in strains of Escherichia coli, the corresponding protein was purified, and its role in rubber degradation was examined by measurement of oxygen consumption as well as by chromatographic and spectroscopic methods. It turned out that active Lcp1VH2 is a monomer and is responsible for the oxidative cleavage of poly(cis-1,4-isoprene) in synthetic as well as in natural rubber by the addition of oxygen (O2) to the cis double bonds. The resulting oligomers possess repetitive isoprene units with aldehyde (CHO-CH2-) and ketone (-CH2-CO-CH3) functional groups at the termini. Two fractions with average isoprene contents of 18 and 10, respectively, were isolated, thus indicating an endocleavage mechanism. The activity of Lcp1VH2 was determined by applying a polarographic assay. Alkenes, acyclic terpenes, or other rubber-like polymers, such as poly(cis-1,4-butadiene) or poly(trans-1,4-isoprene), are not oxidatively cleaved by Lcp1VH2. The pH and temperature optima of the enzyme are at pH 7 and 30°C, respectively. Furthermore, it was demonstrated that active Lcp1VH2 is a Cu(II)-containing oxygenase that exhibits a conserved domain of unknown function which cannot be detected in any other hitherto-characterized enzyme. The results presented here indicate that this domain might represent a new protein family of oxygenases.
Topics: Biotransformation; Chromatography; Coenzymes; Copper; Enzyme Stability; Escherichia coli; Gene Expression; Gordonia Bacterium; Hemiterpenes; Hydrogen-Ion Concentration; Hydrolysis; Latex; Oxygen; Oxygenases; Polarography; Recombinant Proteins; Rubber; Spectrum Analysis; Temperature
PubMed: 24928880
DOI: 10.1128/AEM.01502-14 -
The Journal of Cell Biology Feb 1970In view of the importance of fatty acids as substrates for the mature heart, fatty acid oxidation by fetal and calf heart mitochondria has been investigated. Free fatty...
In view of the importance of fatty acids as substrates for the mature heart, fatty acid oxidation by fetal and calf heart mitochondria has been investigated. Free fatty acids of 10 carbon units or less which exhibit carnitine-independent transport into mitochondria were effective substrates for oxidative phosphorylation in both fetal and calf heart mitochondria. Efficient oxidative phosphorylation with these substrates was dependent upon the presence of bovine serum albumin in the assay medium to reverse the uncoupling effects of the fatty acids. In the presence of bovine serum albumin, ADP/0 ratios were in the range of 3 when short-chain fatty acids and carnitine esters of short- and long-chain fatty acids were substrates. Compared with calf heart mitochondria, fetal heart mitochondria showed decreased carnitine-dependent oxidation of palmityl-CoA. However, the oxidation of palmitylcarnitine was identical in both. These data suggest that the formation of palmitylcarnitine is rate limiting for palmityl-CoA oxidation by the fetal heart mitochondria and that long-chain fatty acids are not readily oxidized by the fetal heart.
Topics: Age Factors; Animals; Animals, Newborn; Biological Transport, Active; Carnitine; Cattle; Coenzyme A; Fatty Acids; Fetus; Growth; Heart; Histocytochemistry; Mitochondria, Muscle; Oxidative Phosphorylation; Oxygen Consumption; Palmitic Acids; Polarography; Serum Albumin, Bovine; Spectrophotometry
PubMed: 5415033
DOI: 10.1083/jcb.44.2.354