Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “OXIDATION REDUCTION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources
PubMedDate not supplied

Oxidation-reduction potential as a control variable for the anaerobic stage during anaerobic-aerobic p-nitrophenol degradation.

Combined anaerobic-aerobic processes are a viable alternative for the treatment of xenobiotic compounds that are difficult to treat by traditional processes. The variable nature of the sequencing batch reactors, SBR, systems allows manipulation of the selective pressure on the microorganisms. Then, the activity of the community can be dynamically adjusted to meet changing effluents conditions. To improve the response of the SBR to changing influent conditions, several efforts have been made to automate and control the duration of the sequential phases of the SBR. The objective of this work is to present and discuss the feasibility of the use of the oxidation-reduction potential, ORP, as a control variable for the determination of the anaerobic phase length in an anaerobic-aerobic SBR used to degrade p-nitrophenol, PNP. The control of the anaerobic phase of the anaerobic-aerobic reactor was achieved with software developed at the Institute of Engineering-UNAM. During the anaerobic stage, the PNP is reduced to p-aminophenol, PAP. As a consequence of the compound transformation, there is a change in the oxidation-reduction potential of the culture medium. This change was used to indicate the minimal concentration of PNP and, as a consequence, the maximal PAP concentration. The feasibility of the algorithm for using the variations in the ORP to determine on-line the length of the anaerobic stage in an anaerobic-aerobic process was demonstrated in our laboratory.

Aerobiosis↗
PubMed1976

Oxidation-reduction properties of several low potential iron-sulfur proteins and of methylviologen.

Apparent oxidation-reduction potentials at pH 7.0 and 25 degrees C were determined using the H2-hydrogenase system with ferredoxins from the following sources: Clostridium pasteurianum, -403 mV; C tartarovorum, -424 mV; C. acidi-urici, -434 mV; Peptococcus aerogenes, -427 mV; Chromatium D, -482 mV (pH 8.0); B. polymyxa, Fd I, -377 mV, and Fd II, -422 mV; and spinach, -428 mV. The pH dependence of these values was variable, ranging from -2 to -24 mV/pH unit increase for different ferredoxins. Over the range of buffer concentrations between 0.05 and 0.2 M, the potentials did not vary significantly. The number of electrons transferred during reduction (as determined by integrations of EPR spectra and by dithionite titration) is 2 for the first five proteins, while potentiometric data for all the cases fit a Nernst equation for which n = 1. The E degrees' value for the redox indicator methylviologen at pH 7.4 was found to be -460 mV, according to both the H2-hydrogenase system and cyclic voltammetry, significantly different from the value previously reported at higher pH's. Additionally, the presence of C. pasteuranum ferredoxin appears to shift the E degrees value of methylviologen to even more negative values. An analysis of sources of error inherent with potential determinations with H2 and hydrogenase is presented. The electronic and EPR spectra of P. aerogenes ferredoxin, for which the x-ray structure has been published, are given here. It appears that the determination of potentials of ferredoxin and other low-potential porteins with the H2-hydrogenase system affords certain experimental advantages over alternative methods currently employed with these and similar substances.

Binding Sites↗
PubMed1977

The pH dependence of the oxidation-reduction midpoint potential of cytochromes c2 in vivo.

A recent report by Pettigrew et al. [Biochim, Biophys. Acta 430, (1976), 197-208] has examined the pH dependence of the oxidation-reduction midpoint potential of cytochromes c2 in vitro. In media of low ionic strength, these workers identified several pKs on the oxidized forms of the cytochromes, and in some cases there were also pKs on the reduced species. In this work we examine the pH dependence of the midpoint potentials of the cytochromes in situ, attached to the chromatophore membrane. Under these conditions no pK values are detected, and we conclude that in vivo there is no net change in the protonation of cytochrome c2 during oxidation or reduction.

Cytochrome c Group↗
PubMed1995

Spectroscopic and kinetic studies on reaction of cytochrome P450nor with nitric oxide. Implication for its nitric oxide reduction mechanism.

Cytochrome P450 purified from Fusarium oxysporum (P450nor) is a unique heme enzyme that catalyzes the reduction of nitric oxide to nitrous oxide with electrons directly transferred from NADH (2NO + NADH + H+--> N2O + H2O + NAD+). We studied the reaction of P450nor with NO and NADH using stopped-flow rapid scan and low temperature spectroscopic methods. The NO ligand can bind to the ferric enzyme to form the stable NO bound complex, P450nor(Fe3+NO). Reduction of P450nor(Fe3+NO) with NADH yielded an intermediate, which transiently formed (tau = approximately 100 ms) and spontaneously decomposed to the Fe3+ state. The optical absorption spectrum of the intermediate was different from that of P450nor(Fe2+NO), which was formed by either a one-electron reduction of P450nor(Fe3+NO) with Na2S2O4 or NO binding to P450nor(Fe2+). On the basis of these observations, we suggested that the intermediate is presumably a two-electron reduced product of P450nor(Fe3+NO) by NADH, formally the (Fe3+NO)2-complex. We determined the rate constants of these reactions at 10 degrees C for the NO binding to P450nor(Fe3+) (2.6 x 10(7) M-1 s-1), the NADH reduction of P450nor(Fe3+NO) (0.9 x 10(6) M-1 s-1), and the spontaneous decomposition of the intermediate (0.027 s-1). In these kinetic measurements, it was found that the former two processes are fast enough, while the latter is extremely slow, compared with the fast turnover of the catalytic reaction (1200 s-1 at 10 degrees C), which we measured by monitoring the NADH consumption. Therefore, we suggested that in the catalytic cycle, decomposition of the intermediate is fairly accelerated by free NO, resulting in such a fast turnover. On the basis of several lines of the spectroscopic and the kinetic evidence, we proposed a possible mechanism of the NO reduction by P450nor.

Cytochrome P-450 Enzyme System↗
PubMed1986

The reduction-oxidation status may influence the degradation of glyceraldehyde-3-phosphate dehydrogenase.

NADH and NADPH accelerate the 'in vitro' rate of proteolysis of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by elastase and other proteases, including lysosomal proteases. NAD+ and NADP+ have the opposite effect. Since there is a good correlation between proteolytic susceptibility of proteins and their 'in vivo' degradation rates, a possible role of the reduction-oxidation status in controlling the intracellular degradation of GAPDH is advanced.

Glyceraldehyde-3-Phosphate Dehydrogenases↗
PubMed1984

Effect of nicotinamide adenine dinucleotide on the oxidation-reduction potentials of lipoamide dehydrogenase from pig heart.

The effect of NAD+ on lipoamide dehydrogenase from pig heart was investigated physicochemically. The observed and theoretical oxidation-reduction mid-point potentials for the oxidized lipoamide dehydrogenase (E)/two-electron-reduced lipoamide dehydrogenase (EH2) couple in the presence on NAD+ were -218 mV and -251 mV, respectively, at pH 6.0. Therefore, unexpectedly the mid-point potential of the enzyme became more positive on NAD+ binding. Decreases in the fluorescence lifetime and intensity and increase in the degree of polarization of enzyme-bound FAD were observed in the presence of NAD+. Fluorescence quenching of bound FAD by NAD+ was released by phenobarbital. The results suggest that NAD+ strengthens the intramolecular dynamic interaction between the isoalloxazine moiety and adenine moiety of bound FAD, and so alters the mid-point potential of the enzyme. These findings indicate that NAD+ acts not only as an acceptor of electrons from EH2, but also as an effector in the flavin-disulfide interaction of EH2.

Animals↗
PubMed1988

Oxidation-reduction thermodynamics of the acceptor quinone complex in whole-membrane fragments from Chloroflexus aurantiacus.

Oxidation-reduction thermodynamic equilibria involving the quinone-acceptor complex have been examined in whole-membrane fragments from Chloroflexus aurantiacus. The primary quinone acceptor was titrated by monitoring the amount of cytochrome c554 photooxidized by a flash of light as a function of the redox potential. In contrast to previous data obtained in purified plasma membranes, in which the primary quinone acceptor exhibited a midpoint potential equal to -50 mV at pH 8.2, in whole-membrane fragments it titrated at -210 mV (pH 8.0), with a pH dependence of -60 mV/pH up to a pK value of 9.3. o-Phenanthroline, an inhibitor of electron transfer from the primary to the secondary quinone acceptor, shifted the Em/pH curve of the primary acceptor to higher redox potentials. The midpoint potential of the secondary quinone acceptor and its dependence on pH has been determined by comparing the kinetics of the charge recombination processes within the reaction center complex in the presence and in the absence of o-phenanthroline. It is concluded that both the primary and the secondary quinone acceptors interact with a proton, with pK values of 9.3 and of approximately 10.2 respectively. At physiological pH the electron appears to be stabilized on the secondary with respect to the primary quinone acceptor by approximately 60 meV.

Bacteria↗
PubMed2000

Oxidation-reduction properties of the regulatory disulfides of sorghum chloroplast nicotinamide adenine dinucleotide phosphate-malate dehydrogenase.

Oxidation-reduction midpoint potentials (E(m)) have been measured for the thioredoxin-dependent, reductive activation of sorghum nicotinamide adenine dinucleotide phosphate- (NADP-) dependent malate dehydrogenase (MDH) in the wild-type enzyme and in a number of site-specific mutants. The E(m) value associated with activation of the wild-type enzyme, -330 mV at pH 7.0, can be attributed to the E(m) of the C365/C377 disulfide present in the C-terminal region of the enzyme. The C24/C29 disulfide, located in the N-terminal region of the enzyme and the only other disulfide present in oxidized, wild-type MDH, has a E(m) value of -280 mV at pH 7.0. A third regulatory disulfide, C24/C207, that is absent in the oxidized enzyme but is thought to be formed during the activation process, has an E(m) value at pH 7.0 of -310 mV. E(m) vs pH profiles suggest pK(a) values for the more acidic cysteine involved in the formation of each of these disulfides of 8.5 for C24/C29; 8.1 for C24/C207; and 8.7 for C365/C377. The results of this study show that the N-terminal disulfide formed between C24 and C29 has a more positive E(m) value than the two other disulfides and is thus is likely to be the "preregulatory disulfide" postulated to function in activating the enzyme.

Alanine↗
PubMed1978

EPR determination of the oxidation-reduction potentials of the hemes in cytochrome c3 from Desulfovibrio vulgaris.

EPR spectroscopy in conjunction with oxidation-reduction potentiometry has been used to determine the half-reduction potentials of the four hemes of cytochrome c3. As predicted, the four hemes of cytochrome c3 have different mid-point potentials. The Em values are: Heme I,--284 mV; Heme II,--310 mV; Heme III,--324 mV and Heme IV,--319 mV. The n-values in each case was near one.

Cytochrome c Group↗
PubMed2005

[Determination of oxidation-reduction level in patients with rheumatoid arthritis].

OBJECTIVE: To examine the oxidation or reduction products in patients with rheumatism arthritis (RA), and investigate the relationship between oxidation or reduction products and occurrence and development of RA. METHODS: The serum levels of total ascorbic acid (TAA), dehydroascorbic acid (DHAA)/TAA, vitamin E, advanced oxidation protein products (AOPP) and malondialdehyde (MDA) were detected by high-performance liquid chromatography with electrochemical detection in 83 RA patients and 30 healthy adults. Correlation analysis of AOPP, MDA and hs-CRP was performed. RESULTS: Compared with normal control group, significantly higher serum MDA, DHAA/TAA, and AOPP levels were detected in RA patients (P<0.05), but vitamin E showed no significant difference (P<0.05). Linear regression analysis showed that MDA (P<0.01) was positively but AOPP (P>0.05) negatively correlated to hs-CRP. CONCLUSIONS: Oxidation or reduction products in serum of RA patients increases significantly, which may be an important mechanism for the occurrence and development of RA. Serum AOPP and MDA levels can reflect the oxidation status in RA patients.

Adult↗
PubMed1989

Oxidation-reduction potentials and ionization states of extracellular peroxidases from the lignin-degrading fungus Phanerochaete chrysosporium.

The oxidation-reduction potentials of lignin peroxidase isozymes H1, H2, H8, and H10 as well as the Mn-dependent peroxidase isozymes H3 and H4 are reported. The potentiometric titrations involving the ferrous and ferric states of the enzyme had Nernst plots indicating single-electron transfer. The Em7 values of lignin peroxidase isozymes H1, H2, H8, and H10 are -142, -135, -137, and -127 mV versus standard hydrogen electrode, respectively. The Em7 values for the Mn-dependent peroxidase isozymes H3 and H4 are -88 and -93 mV versus standard hydrogen electrode, respectively. The midpoint potential of H1, H8, and H4 remained unchanged in the presence of their respective substrates, veratryl alcohol and Mn(II). The midpoint potential between the ferric and ferrous forms of isozymes H1 and H4 exhibited a pH-dependent change between pH 3.5 and pH 6.5. These results indicate that the reductive half-reaction of the enzymes is the following: ferric peroxidase + le- + H+----ferrous peroxidase. Above pH 6.5, the effect of pH on the midpoint potential is diminished and indicates that an ionization with an apparent pKa equal to approximately 6.6-6.7 occurs in the reduced form of the enzymes. A heme-linked ionization group in the ferrous form of the enzymes was confirmed by studying the effect of pH on the absorption spectra of isozymes H1 and H4. These spectrophotometric pH titration experiments confirmed the electrochemical results indicating pKa values of 6.59 and 6.69 for reduced isozymes H1 and H4, respectively. These results indicate the presence of a heme-linked ionization of an amino acid in the reduced form of the lignin peroxidase isozymes similar to that of other plant peroxidases.

Basidiomycota↗
PubMed1978

The electronic state of heme in cytochrome oxidase II. Oxidation-reduction potential interactions and heme iron spin state behavior observed in reductive titrations.

Magnetic circular dichroism (MCD), electron paramagnetic resonance (EPR), and optical absorption spectroscopies have been used to monitor the concentrations of oxidized and reduced heme and copper during stoichiometric reductive titrations of purified beef heart cytochrome oxidase. The MCD data are deconvoluted to obtain the concentrations of reduced cytochromes a and a3 during the titrations; analysis of the EPR spectra provides complementary data on the concentrations of the EPR-detectable species. For the native enzyme in the absence of exogenous ligands, cytochromes a and a3 are reduced to approximately the same extent at all points in the titration. The reduction of the EPR-detectable copper, on the other hand, initially lags the reduction of the two cytochromes but in the final stages of the titration is completely reduced prior to either cytochrome a or a3. These non-Nernstian titration results are interpreted to indicate that the primary mode of heme-heme interaction in cytochrome oxidase involves shifts in oxidation-reduction potential for each of the two cytochromes such that a change in oxidation state for one of the hemes lowers the oxidation-reduction potential of the second heme by approximately 135 mV. In these titrations high spin species are detected which account for 0.25 spin/oxidase maximally. Evidence is presented to indicate that at least some of these signals can be attributed to cytochrome a3+ which has undergone a low-spin to high-spin state transition in the course of the titration. In the presence of carbon monoxide the oxidation-reduction properties of cytochromes a and a3 are markedly altered. The a32+. CO complex is fully formed prior to reduction of either cytochrome a3+ or the EPR-detectable copper. The g = 3 EPR signal attributed to cytochrome a3+ decreases as the MCD intensity of cytochrome a2+ increases; no significant high-spin intensity is observed at any intermediate stage of reduction. We interpret these Nernstian titration results to indicate that in the presence of ligands the oxidation-reduction potential of cytochrome a relative to cytochrome a3 is determined by the oxidation-reduction state of the stabilized cytochrome a3 ligand complex; if ligand binding occurs to reduced cytochrome a3 then cytochrome a titrates with a lower potential; cytochrome a titrates with a higher potential if oxidized cytochrome a3 is stabilized by ligand binding.

Animals↗
PubMed1990

[Oxidation-reduction properties of compounds containing the alpha-ketoendiolic system in the molecule].

The performed investigations covered the reducing-oxidizing properties of five selected analogues of L-ascorbic acid (those of acids: D-arabo-, L-arabo-, D-oxylo-, D-gluco and D-galactoascorbic). Due to the fact that alpha-ketonendiolic system appears in their molecules, the character of these compounds is that of medium strength acids, and they concurrently show distinct reducing-oxidizing properties. The studied compounds were obtained by resorting to synthesis. Their reducing properties were estimated on the basis of determined static and kinetic parameters. In the first group of tests, concentration-activity dissociation constant of first and second steps k'1,2 as well as formal normal oxidation-reduction potentials E'2, corresponding to the conditions of total ionization of the studied systems, were determined for all the acids. The example of L-ascorbic acid was used to define the dependence of dissociation constant values on temperature and ionic strength of the medium. Calculation was made to establish effective diameters of ion reactions occurring in the medium as well as standard enthalpies for both dissociation steps. In the other group of tests the second order rate constants k"0 in reaction of potassium ferricyanide and cytochrome c reduction were determined for all the studied compounds. Ionic strength effect on kinetics of both reactions was investigated, using L-ascorbic acid as a model system. In consequence of the performed studies it has been ascertained that, under conditions almost similar to physiological ones (pH, ionic strength, temperature) the dinegative ions of all the tested acids are the main, reduction-active, form. Their absolute reduction power is as follows, acid: L-ascorbic greater than D-iso- greater than D-gluco- greater than D-galactoascorbic. The results of the accomplished studies confirm the close association of reducing-oxidizing properties of the studied compounds with their acidic properties. The acids, more readily undergoing total dissociation, are characterized by greater durability of reduced forms. In the pH range from 4 to 7, both of ascorbinate ions take parallel part in the reactions. However, the principal share of dinegative ions is characteristic of reactions proceeding in media with pH 7.

Ascorbic Acid↗
PubMed1971

The Respiratory Chain of Plant Mitochondria: IX. Oxidation-Reduction Potentials of the Cytochromes of Mung Bean Mitochondria.

The oxidation-reduction potentials of the cytochromes of the respiratory chain of mung bean (Phaseolus aureus) mitochondria have been measured under strictly anaerobic conditions with a combined spectrophotometric/potentiometric method. The midpoint potentials at pH 7.2 are as follows: cytochrome a: +190 millivolts; a(3): +380 millivolts; b(553): +75 millivolts; b(557): +42 millivolts; b(562): -77 millivolts; c(547) and c(549): +235 millivolts. (The subscripts refer to the difference absorbance maxima observed for these cytochromes in reduced-minus-oxidized difference spectra recorded at 77 K.) The same values of midpoint potentials at pH 7.2 are obtained with mitochondria depleted of energy by aerobic incubation with ADP and uncoupler in the presence of inorganic phosphate, or with coupled mitochondria energized with ATP in the absence of inorganic phosphate. Coupling site II is placed between b(553)/b(557) and c(549)/c(547) in these mitochondria, and coupling site III is placed between a and a(3).

Journal Article↗
PubMed1982

The oxidation-reduction kinetics of the reaction of cytochrome c1 with non-physiological redox agents.

The kinetics of the oxidation-reduction reactions of cytochrome c1 with ascorbate, ferricyanide, triphenanthrolinecobalt(III) and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) have been examined using the stopped-flow technique. The reduction of ferricytochrome c1 by ascorbic acid is investigated as a function of pH. It is shown that at neutral and alkaline pH the reduction of the protein is mainly performed by the doubly deprotonated form of ascorbate. From the ionic-strength-dependence studies of the reactions of cytochrome c1 with ascorbate, ferricyanide and triphenanthrolinecobalt(III), it is demonstrated that the reactions rate is governed by electrostatic interactions. The second-order rate constants for the reaction of cytochrome c1 with ascorbate, ferricyanide, TMPD and triphenanthrolinecobalt(III) are 1.4 . 10(4), 3.2 . 10(3), 3.8 . 10(4) and 1.3 . 10(8) M-1 . s-1 (pH 7.9, I = 0, 10 degrees C), respectively. Application of the Debye-Hückel theory to the data of the ionic-strength-dependence studies of these redox reactions of cytochrome c1 yielded for ferrocytochrome c1 and ferricytochrome c1 a net charge of --5 and --4, respectively. The latter value is close to that of --3 for the oxidized enzyme, calculated from the amino acid sequence of the protein. This implies that not a local charge on the surface of the protein, but the overall net charge of cytochrome c1 governs the reaction rate with small redox molecules.

Animals↗