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PubMed1991

Polycyclic aromatic hydrocarbon quinone-mediated oxidation reduction cycling catalyzed by a human placental NADPH-linked carbonyl reductase.

Polycyclic aromatic hydrocarbon quinones, hydroquinones, and glutathionyl adducts of quinones undergo oxidation-reduction (redox) cycling in the presence of NADPH and the NADPH-linked human placental carbonyl reductase. K-region and non-K-region o-quinones and their glutathione adducts are the best substrates of this enzyme; they are reduced to hydroquinones. Under aerobic conditions, the hydroquinones are autoxidized with the formation of potentially hazardous semiquinones and the superoxide anion. Because of these reactions it is unlikely that polycyclic aromatic hydrocarbon quinones or their glutathione adducts are inert products of detoxication in tissues that contain the carbonyl reductase or another enzyme with similar substrate specificity. If superoxide dismutase is added to reaction mixtures containing the carbonyl reductase and quinones, it inhibits redox cycling. Presumably this results from destruction of the superoxide anion which acts as a chain propagator in these reactions.

Alcohol Oxidoreductases↗
PubMed1976

Blockage by acetylene of nitrous oxide reduction in Pseudomonas perfectomarinus.

Suspensions of denitrifying cells of Pseudomonas perfectomarinus reduced nitrate and nitrate as expected to dinitrogen; but, in the presence of acetylene, nitrous oxide accumulated when nitrate or nitrate was reduced. When supplied at the outset in place of nitrate and nitrate, nitrous oxide was rapidly reduced to dinitrogen by cells incubated in anaerobic vessels in the absence of acetylene. In the presence of 0.01 atmospheres of acetylene, however, nitrous oxide was not reduced. Ethylene was not produced, nor did it influence the rate of nitrous oxide reduction when provided instead of acetylene. Cells exposed to 0.01 atmospheres of acetylene for as long as 400 min were able to reduce nitrous oxide after removal of acetylene at a rate comparable to that of cells not exposed to acetylene. Acetylene did not affect the production or functioning of assimilatory nitrate or nitrite reductase in axenic cultures of Enterobacter aerogenes or Trichoderma uride. While exposed to acetylene, bacteria in marine sediment slurries produced measurable quantities of nitrous oxide from glucose- or acetate-dependent reduction of added nitrate. Possible use of acetylene blockage for measurement of denitrification in unamended marine sediments is discussed.

Acetylene↗
PubMed1981

Oxidation-reduction properties of the cytochrome b found in the plasma-membrane fraction of human neutrophils. A possible oxidase in the respiratory burst.

The oxidation-reduction midpoint potential of the cytochrome b found in the plasma membrane of human neutrophils has been determined at pH 7.0 (Em,7.0) from measurements of absorption spectra at fixed potentials. In both unstimulated and phorbol myristate acetate-stimulated cells Em,7.0 was -245 mV. Changes in pH affected the Em of the cytochrome b, with a slope of approx. 25 mV/pH unit change. The Em,7.0 of the haem group(s) of the membrane-bound myeloperoxidase of human neutrophils was found to be +34 mV. The plasma membranes contained no detectable ubiquinone, and no iron-sulphur compounds were detected by e.p.r. spectroscopy at 5-20 K. No flavins were detected by e.p.r. spectroscopy. The cytochrome b-245 was not reduced by added NADH or NADPH. Dithionite-reduced cytochrome b-245 formed a complex with CO, supplied as a saturated solution, which was dissociated with 26 microseconds illumination from a xenon flash lamp, and the recombination with CO had a half-time of approx. 6 ms. Partly (80%) reduced cytochrome b-245 was oxidized by added air-saturated buffer with a half-time faster than 1 s at 20 degrees C, a resolution limited by mixing time. These results are compatible with cytochrome b-245 acting as an oxidase.

Cell Membrane↗
PubMed1977

The oxidation-reduction potential of the reaction-centre chlorophyll (P700) in Photosystem I. Evidence for multiple components in electron-paramagnetic-resonance signal 1 at low temperature.

The oxidation-reduction potential of the reaction-centre chlorophyll of Photosystem I (P700) in spinach chloroplasts was determined by using the ability of the reaction centre to photoreduce the bound ferredoxin and to photo-oxidize P700 on illumination at 20K as an indicator of the oxidation state of P700. This procedure shows that P700 is oxidized with Em (pH8.0)(mid-point redox potential at pH8.0)congruent to +375mV. Further oxidation of the chloroplast preparations by high concentrations of K3Fe(CN)6(10mM) in the presence of mediating dyes leads to the appearance of a large radical signal with an apparent Em congruent to +470mVA second, light-inducible, radical also appears over the same potential range. We propose that these signals are due to bulk chlorophyll oxidation and not, as was previously thought [Knaff & Malkin (1973) Arch. Biochem. Biophys. 159, 555-562], to reaction-centre oxidation. A number of optical techniques were used to determine Em of P700. Dual-wavelength spectroscopy (697-720nm) indicates Em congruent to +460-+480mV. The spectrum of the sample during the titration showed a large contribution to the signal by bulk chlorophyll oxidation, in agreement with the electron-paramagnetic-resonance results and those of Ke, Sugahara & Shaw [(1975) Biochim. Biophys. Acta 408, 12-25]. The light-induced absorbance change at 435 nm, usually attributed to P700, showed a potential dependence similar to that of bulk chlorophyll oxidation. Determination of Em of P700 on the basis of the appearance of the P700 signal in oxidized-versus-reduced difference spectra showed Em (pH8.0) congruent to +360mV. Measurements of the effect of potential on the irreversible photo-oxidation of P700 at 77K showed that P700 became oxidized in this potential range. We conclude that the reaction-centre chlorophyll of Photosystem I has Em (pH8.0) congruent to +375mV.

Chlorophyll↗
PubMed1984

The influence of oxidation-reduction state on the kinetic stability of pig kidney general acyl-CoA dehydrogenase and other flavoproteins.

Pig kidney general acyl-CoA dehydrogenase is markedly stabilized against loss of flavin and activity in 7.3 M-urea or at 60 degrees C upon reduction with sodium dithionite or octanoyl-CoA. Electron transferring flavoprotein is similarly stabilized, whereas egg white riboflavin-binding protein loses flavin more readily on reduction. These and other data support the anticipated correlation between the kinetic stability of the holoproteins and the oxidation-reduction potential of their bound flavins.

Acyl Coenzyme A↗
PubMed1997

Modulation of potassium channel function by methionine oxidation and reduction.

Oxidation of amino acid residues in proteins can be caused by a variety of oxidizing agents normally produced by cells. The oxidation of methionine in proteins to methionine sulfoxide is implicated in aging as well as in pathological conditions, and it is a reversible reaction mediated by a ubiquitous enzyme, peptide methionine sulfoxide reductase. The reversibility of methionine oxidation suggests that it could act as a cellular regulatory mechanism although no such in vivo activity has been demonstrated. We show here that oxidation of a methionine residue in a voltage-dependent potassium channel modulates its inactivation. When this methionine residue is oxidized to methionine sulfoxide, the inactivation is disrupted, and it is reversed by coexpression with peptide methionine sulfoxide reductase. The results suggest that oxidation and reduction of methionine could play a dynamic role in the cellular signal transduction process in a variety of systems.

Amino Acid Sequence↗
PubMed1990

Measurement of oxidation-reduction midpoint potentials by room temperature electron paramagnetic resonance potentiometry.

A room temperature electron paramagnetic resonance potentiometric cell has been developed for the measurement of oxidation-reduction midpoint potentials of enzymes containing paramagnetic centers. Based upon an aqueous flat cell designed for use with the Varian TM high sensitivity cavity, the apparatus combines a high degree of anaerobiosis with low volume requirements. The cell is simple in design, easily constructed, and can be adapted for use with most spectrometer cavities. Tests of the cell using xanthine oxidase, in 50 mM Bicine buffer, pH 7.7, yielded midpoint potentials of -345 and -371 mV for the Mo(VI)/Mo(V) and Mo(V)/Mo(IV) couples compared with values of -373 and -377 mV obtained by electron paramagnetic resonance analysis of frozen potentiometric samples. These values indicate that shifts, of the order of 20-40 mV, may occur upon freezing poised samples. For the Mo center of xanthine oxidase, these shifts in potential are more pronounced for the Mo(VI)/Mo(V) couple and result in a destabilization of the Mo(V) intermediate during freezing.

Animals↗
PubMed1978

Oxidation-reduction midpoint potentials of mitochondrial flavoproteins and their intramitochondrial localization.

Spectrophotometric and fluorimetric substrate couple titrations and potentiometric spectrophotometric titrations were used to determine the oxidation-reduction potentials of components showing absorbance or fluorescence at the wavelengths attributable to the flavoproteins of mitochondria fractionated using digitonin together with sonication. A pure mitoplast fraction devoid of cytochrome b5 contamination could be obtained using 230 micrograms digitonin/mg of mitochondrial protein. The digitonin-soluble fraction contained a species having Em7.4 = -123 mV and probably represents the outer membrane flavoproteins. The inner membrane-matrix fraction, treated with ultrasound, provided evidence of a flavoprotein species with redox potential (Em7.4 = -302 mV) in the matrix fraction. The -302 mV component is probably lipoamide dehydrogenase. A high redox potential species with Em7.4 = +19 mV in titrations with the succinate fumarate couple was located in the inner membrane vesicles and is probably identical with succinate dehydrogenase. The electron-transferring flavoprotein (ETF) was isolated from bovine heart mitochondria and its Em7.4 = -74 mV determined. The component in the matrix fraction with an apparent Em7.4 = -56 mV probably represents ETF, and that in the inner membrane fraction with an apparent Em7.4 = -43 mV the NADH dehydrogenase flavoprotein. A component in an apparently low concentration with Em7.4 = +30 mV was detected in the inner membrane fraction. This probably represents the ETF-dehydrogenase flavoprotein. The origin of the flavoprotein fluorescence of mitochondria and intact tissues is discussed.

Animals↗
PubMed1991

Oxidation-reduction potentials of ferredoxin-NADP+ reductase and flavodoxin from Anabaena PCC 7119 and their electrostatic and covalent complexes.

The oxidation-reduction potentials of ferredoxin-NADP+ reductase and flavodoxin from the cyanobacterium Anabaena PCC 7119 were determined by potentiometry. The potentials at pH 7 for the oxidized flavodoxin/flavodoxin semiquinone couple (E2) and the flavodoxin semiquinone/hydroquinone couple (E1) were -212 mV and -436 mV, respectively. E1 was independent of pH above about pH 7, but changed by approximately -60 mV/pH below about pH 6, suggesting that the fully reduced protein has a redox-linked pKa at about 6.1, similar to those of certain other flavodoxins. E2 varied by -50 mV/pH in the range pH 5-8. The redox potential for the two-electron reduction of ferredoxin-NADP+ reductase was -344 mV at pH 7 (delta Em = -30 mV/pH). In the 1:1 electrostatic complex of the two proteins titrated at pH 7, E2 was shifted by +8 mV and E1 was shifted by -25 mV; the shift in potential for the reductase was +4 mV. The potentials again shifted following treatment of the electrostatic complex with a carbodiimide, to covalently link the two proteins. By comparison with the separate proteins at pH 7, E2 for flavodoxin shifted by -21 mV and E1 shifted by +20 mV; the reductase potential shifted by +2 mV. The potentials of the proteins in the electrostatic and covalent complexes showed similar pH dependencies to those of the individual proteins. Qualitatively similar changes occurred when ferredoxin-NADP+ reductase from Anabaena variabilis was complexed with flavodoxin from Azotobacter vinelandii. The shifts in redox potential for the complexes were used with previously determined values for the dissociation constant (Kd) of the electrostatic complex of the two oxidised proteins, in order to estimate Kd values for the interaction of the different redox forms of the proteins. The calculations showed that the electrostatic complexes, formed when the proteins differ in their redox states, are stronger than those formed when both proteins are fully oxidized or fully reduced.

Anabaena↗
PubMed1980

[The effect of alcohol and alcohol withdrawal therapy on the concentration of carbohydrate products of metabolism and electrolytes (Na, K, Mg, Cl) in the blood and cerebrospinal fluid--changes in the oxidation-reduction in the brain].

Both ethanol and ethanol-disulfiram reaction result in a lactacidosis of CSF. The Disulfiram produces hyperglycorhachia, the ethanol causes a shift of the oxidation-reduction processes in the direction to reduction. The Apomorphine has no side effects. The various treatments of alcoholics do not influence the electrolyte concentrations in the CSF.

Adult↗
PubMed2005

Synthesis of polyhydroxyalkanoate (PHA) from excess activated sludge under various oxidation-reduction potentials (ORP) by using acetate and propionate as carbon sources.

Accumulation of poly hydroxyalkanoate (PHA) from excess activated sludge (EAS) was monitored and controlled via the oxidation-reduction potential (ORP) adjusting process. The ORP was adjusted and controlled by only regulating the gas-flow rate pumped into the cultural broth in which sodium acetate (C2) and propionate (C3) were used as carbon sources. Productivity of PHA and the PHA compositions at various C2 to C3 ratios were also investigated. When ORP was maintained at +30 mV, 35% (w/w) of PHA of cell dry weight obtained when C2 was used as sole carbon source. The PHA copolymer, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), accumulated by EAS with different 3-hydroxyvalarate (3HV) molar fractions ranged from 8% to 78.0% when C2 and C3 was used as sole carbon source, By using ORP to monitor and control the fermentation process instead DO meter, the ORP system provided more precise control to the PHA accumulation process from EAS under low dissolved oxygen (DO) concentrations. Adjusting the C2 to C3 ratios in the media could control the composition such as the 3HV/3HB ratios of the PHBV. Furthermore, it might be an effective way to adjust the 3HV molar fractions in PHBV by controlling the DO concentration via the ORP monitoring system. The 3HV molar fractions in the PHBV declined with increasing ORP from -30 mV to +100 mV by adjusting the gas-flow rate (i.e. the DO concentration). It is concluded that the DO plays a very important role in the synthesis of 3HV subunits in PHBV co-polymer from the EAS. Therefore, a hypothetic metabolic model for PHA synthesis from EAS was proposed to try to explain the results in this study.

Acetates↗
PubMed1987

Oxidation-reduction reactions of cytochrome b6 in a liposome-incorporated cytochrome b6-f complex.

The chloroplast cytochrome b6-f complex, incorporated into phospholipid vesicles, shows proton translocation with an observed H+/e- ratio of approximately 2. The oxidation-reduction behavior of cytochrome b6 during electron transport from duroquinol to plastocyanin is affected by incorporation. The most obvious effect of incorporation is an increase in the duration of a steady-state level of cytochrome b6 that persists during electron transport. Reagents that decrease activity increase the duration of the steady state while reagents that stimulate activity decrease this time. Uncoupling conditions yield cytochrome kinetics similar to those in the unincorporated complex. 2,5-Dibromo-3-methyl-6-isopropyl-p-benzoquinone and 5-n-undecyl-4,7-dioxobenzothiazole inhibited reduction of cytochrome b6 in the incorporated complex, but this apparent inhibition was due to a rapid oxidation of the cytochrome by these compounds.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1996

Oxidation-reduction and transient kinetic studies of spinach ferredoxin-dependent glutamate synthase.

Spinach leaf ferredoxin-dependent glutamate synthase has been shown to contain one FMN but no FAD. The oxidation-reduction midpoint potentials of the FMN and the other prosthetic group, a [3Fe-4S]1+,0 cluster, have both been estimated to be -225 mV by cyclic voltammetry. Confirmation of the isopotential nature of the two prosthetic groups of the enzyme has been obtained using deazariboflavin phototitrations. Flash photolysis measurements have allowed determination of the second-order rate constants for reduction of both of the prosthetic groups of the enzyme by the 5-deazariboflavin semiquinone radical.

Amino Acid Oxidoreductases↗
PubMed1987

Changes in oxidation reduction potentials and volatile fatty acid production by rumen bacteria when methane synthesis is inhibited.

Rumen inoculum was cultured in specially designed fermenters that allowed simultaneous measurement of pH, oxidation-reduction potentials, and gas production. The cultures were maintained at pH 6.8 by addition of 1 M NaHCO3 and continuous infusion of artificial saliva. Gas flow was maintained at 20.0 ml/min with a stream of O2-free N2. Monensin at 7.0 micrograms/ml inhibited CH4 production 49% below control concentrations. The sodium salt of 2-bromoethanesulfonic acid added at an initial concentration of 5 x 10(-5) M inhibited CH4 production by 86% and increased H2 production from less than .5 mumol/min in the control to 24.5 mumol/min in the inhibited fermenter. The redox potentials in the control fermenter remained above -.20 V and did not change with the addition of monensin. Bromoethanesulfonic acid rapidly decreased the redox potential in the fermenter to -.33 V. Volatile fatty acid production was not significantly altered by the addition of 2-bromoethanesulfonic acid. The addition of monensin gave the expected decrease in acetate:propionate ratios, decreased acetate and butyrate production, and increased valerate (but not propionate) production.

Alkanesulfonates↗
PubMed1981

Oxidation-reduction titration of cytochrome components in the electron transport chaim of Azotobacter vinelandii.

The multiple cytochrome components in the electron transport particle of Azotobacter vinelandii were resolved and their oxidation-reduction midpoint potentials were determined by a simultaneous potentiometric and absorption measurements under anaerobic condition with or without CO. The midpoints of the individual cytochrome component corresponding to the membrane-bound types were also determined in the solubilized fractions prepared by a differential detergent solubilization of the membrane particles of A vinelandii. Two cytochromes of b type, one with an absorption maximum measured at 559 nm and another at 561 nm in the membrane particle, were resolved and their Em, 7.4 values determined to be - 30 mV and +122mV, respectively. Cytochrome b 559 reacted in both membrane-bound and solubilized forms, however, cytochrome b561 was inert to CO treatment. Only one cytochrome of c type (c4) measured at 575-551 nm was resolved, its midpoint potential at pH 7.4 was +322mV in the membrane-bound form and +278mV in the solubilized form. This c-type cytochrome had no CO reactivity. Cytochrome d, a CO-reactive component, had a midpoint of +270mV in the membrane fraction. The midpoint of cytochrome a1 in its membrane-bound form could not be measured accurately because of its low concentration. However, in the solubilized preparations, cytochrome a1 apparently had a red shift with an absorption maximum at 613 nm, with an estimated Em, 7.4 of - 45 mV, while cytochrome d was no longer detected, possibly because of denaturation.

Azotobacter↗