scholarly journals The oxidation-reduction potentials of cytochrome o + c4 and cytochrome o purified from Azotobacter vinelandii

1979 ◽  
Vol 181 (3) ◽  
pp. 763-766 ◽  
Author(s):  
T Yang ◽  
D O'Keefe ◽  
B Chance
Keyword(s):  
Azotobacter Vinelandii ◽  
Anaerobic Conditions ◽  
Midpoint Potential ◽  
Reduction Potentials ◽  
Cytochrome O ◽  
Oxidation Reduction ◽  
Ph Range

Oxidation-reduction titrations of Azotobacter vinelandii cytochrome o + c4 and cytochrome o were performed with simultaneous potential and absorbance measurements under anaerobic conditions. Cytochrome c4 has a midpoint potential (Em, 7.4) of 260mV and purified cytochrome o has an Em, 7.4 of −18mV. Little change in the midpoint potential of cytochrome o was observed when titrated in the pH range 6.2–9.8.

Potentiometric and spectroscopic properties of the cytochrome o complex of Escherichia coli

1990 ◽  
Vol 68 (1) ◽  
pp. 83-90 ◽  
Author(s):  
H. Keith Withers ◽  
Philip D. Bragg
Keyword(s):  
Escherichia Coli ◽  
Absorption Maximum ◽  
Distinct Species ◽  
Spectroscopic Properties ◽  
Alpha Band ◽  
Difference Spectra ◽  
Midpoint Potential ◽  
Reduction Potentials ◽  
Cytochrome O ◽  
Oxidation Reduction

Cytochrome o purified from cell membranes of Escherichia coli shows two potentiometrically distinct species with midpoint oxidation–reduction potentials of + 265 ± 5 and + 140 ± 15 mV. The component with the higher potential reacted with carbon monoxide and so likely is the oxygen-reacting heme of the cytochrome o complex. It appears to be responsible for the absorption maximum at 564 nm in reduced minus oxidized difference spectra measured at 77 K. The midpoint potential of the other component was sensitive to oxidation by ferricyanide. This latter component had an absorption maximum at about 554 nm. The inhibitor 2-heptyl-4-hydroxyquinoline N-oxide inhibited reoxidation of reduced cytochrome o by oxygen and modified the spectroscopic behaviour of the 564 nm component. The ratio of the heights of the maxima in the alpha-band region of the absorption spectrum differed in cytochrome o prepared from cloned material from that found in cytochrome o from noncloned sources, in spite of the similar polypeptide compositions of the two preparations.Key words: cytochrome o, potentiometry, HOQNO (2-heptyl-4-hydroxyquinoline N-oxide), oxidase, respiratory chain.

Oxidation–reduction titration of cytochrome components in the electron transport chain of Azotobacter vinelandii

1981 ◽  
Vol 59 (2) ◽  
pp. 137-144 ◽  
Author(s):  
Tsanyen Yang
Keyword(s):  
Electron Transport ◽  
Cytochrome B ◽  
Absorption Maximum ◽  
Azotobacter Vinelandii ◽  
Reactive Component ◽  
Midpoint Potential ◽  
Oxidation Reduction ◽  
Membrane Bound ◽  
The Individual ◽  
Cytochrome D

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 +122 mV, respectively. Cytochrome b559 reacted with CO readily 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 +322 mV in the membrane-bound form and +278 mV in the solubilized form. This c-type cytochrome had no CO reactivity. Cytochrome d, a CO-reactive component, had a midpoint of +270 mV 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.

scholarly journals Electron-paramagnetic-resonance measurements of the electron-transfer components of the reaction centre of Rhodopseudomonas viridis. Oxidation–reduction potentials and interactions of the electron acceptors

1979 ◽  
Vol 182 (2) ◽  
pp. 515-523 ◽  
Author(s):  
A. William Rutherford ◽  
Peter Heathcote ◽  
Michael C. W. Evans
Keyword(s):  
Reaction Centre ◽  
Double Reduction ◽  
Complex Situation ◽  
Paramagnetic Resonance ◽  
Rhodopseudomonas Viridis ◽  
Midpoint Potential ◽  
Reduction Potentials ◽  
Oxidation Reduction ◽  
Iron Form ◽  
Primary Acceptor

Oxidation–reduction potentiometry was carried out on Rhodopseudomonas viridis chromatophores. Measurements of e.p.r. signals of the semiquinone–iron type at g=1.82 have revealed a more complex situation than previously reported. The presence of three different components is indicated. The midpoint potential (Em) of the primary acceptor quinone/semiquinone couple was found to be approx. −165mV at pH10, with a pK being reached at around pH7.5. The primary acceptor also accepts a second electron with an Em of −525mV, but this redox transition exhibits a hysteresis effect. Interaction effects indicate the presence of another component with Em values at pH10 of approx. −165mV (pK reached at around pH7.5) for single reduction and −350mV (pK at pH10 or greater) for double reduction. It is suggested that this component is the secondary acceptor. Another semiquinone–iron-type component which gives a g=1.82 signal is also present. This component is distinguishable from the primary acceptor by its e.p.r. spectrum, which shows a double peak at g=1.82 and a gx line at g=1.76. This component has Em values at pH10 for single and double reduction of −15mV and approx. −150mV respectively. Both of these Em values are pH-dependent. The presence of an interaction between this component and the photoreduced primary acceptor indicates the close proximity of these components. However, the midpoint potential of this component indicates a function as a secondary electron-transport component rather than an electron acceptor in the reaction centre. The dependence of the bacteriopheophytin intermediate (I) doublet e.p.r. signal on the presence of the semiquinone–iron form of the primary acceptor is demonstrated. The midpoint potential of the I/I− couple is estimated to be lower than −600mV.

125. Technique for obtaining Anaerobic Milk, with some Observations on its CO2 Content

1936 ◽  
Vol 7 (1) ◽  
pp. 25-28 ◽  
Author(s):  
Christopher James Jackson
Keyword(s):  
Blood Plasma ◽  
Gas Analysis ◽  
Anaerobic Conditions ◽  
Reduction Potentials ◽  
Oxidation Reduction

1. A method has been described for obtaining milk anaerobically from the udder.2. A technique for transferring anaerobically drawn milk to an electrode vessel for the determination of oxidation-reduction potentials under anaerobic conditions has been described.3. A technique for transferring anaerobically drawn milk to a van Slyke apparatus for gas analysis has been described.4. The total CO2 of cows’ milk is about half that of their blood plasma.

scholarly journals Oxidation-reduction studies of the Mo-(2Fe-2S) protein from Desulfovibrio gigas

1978 ◽  
Vol 173 (2) ◽  
pp. 419-425 ◽  
Author(s):  
J J G Moura ◽  
A V Xavier ◽  
R Cammack ◽  
D O Hall ◽  
M Bruschi ◽  
...  
Keyword(s):  
Reduction Potential ◽  
Type I ◽  
Midpoint Potential ◽  
Desulfovibrio Gigas ◽  
Reduction Potentials ◽  
Point Potential ◽  
Oxidation Reduction ◽  
Reducing Conditions ◽  
Oxidation Reduction Potential ◽  
Type Ia

Potentiometric titration followed by e.p.r. measurements were used to determine the midpoint reduction potentials of the redox centres of a molybdenum-containing iron-sulphur protein previously isolated from Desulfovibrio gigas, a sulphate-reducing bacterium (Moura, Xavier, Bruschi, Le Gall, Hall & Cammack (1976) Biochem. Biophys. Res. Commun. 728 782-789; Moura, Xavier, Bruschi, Le Gall & Cabral (1977) J. Less Common Metals 54, 555-562). The iron-sulphur centres could readily be distinguished into three types by means of g values, temperature effect, oxidation-reduction potential values and reduction rates. The type-I Fe-S centres are observed at 77 K. They show mid-point potential values of −260mV (Fe-S type IA) and −440 mV (Fe-S type IB). Centres of types IA and IB appear to have similar spectra at 77 K and 24 K. The Fe-S type-II centres are only observed below 65 K and have a midpoint potential of −28mV. Long equilibration times (30 min) with dye mediators under reducing conditions were necessary to observe the very slow equilibrating molybdenum signals. The potential values associated with this signal were estimated to be approx. −415 mV for Mo(VI)/Mo(V) and-530mV for Mo(V)/Mo(IV).

scholarly journals Measurement of the oxidation-reduction potentials for one-electron and two-electron reduction of electron-transfer flavoprotein from pig liver

1984 ◽  
Vol 219 (3) ◽  
pp. 1043-1047 ◽  
Author(s):  
M Husain ◽  
M T Stankovich ◽  
B G Fox
Keyword(s):  
Electron Transfer ◽  
Pig Liver ◽  
Electron Transfer Flavoprotein ◽  
Midpoint Potential ◽  
Potentiometric Titrations ◽  
Reduction Potentials ◽  
Oxidation Reduction ◽  
Electron Reduction ◽  
Reducing Equivalents

Potentiometric titrations of pig liver electron-transfer flavoprotein (ETF) were performed at pH 7.5 and 4 degrees C, both in the reductive and oxidative directions. Reduction of ETF to the hydroquinone form required a total of two reducing equivalents/mol of ETF with the formation of sub-stoichiometric amounts of anionic semiquinone as an intermediate. The oxidation-reduction potentials for the two one-electron couples, oxidized ETF/ETF semiquinone and ETF semiquinone/fully reduced ETF, are +4 mV and -50 mV respectively. The overall midpoint potential for the two-electron couple (oxidized ETF/fully reduced ETF) is -23 mV.

MEASUREMENT OF OXIDATION–REDUCTION CONDITIONS IN WHEAT LEAF SAP BY A POTENTIOMETRIC METHOD

1960 ◽  
Vol 38 (3) ◽  
pp. 387-398 ◽  
Author(s):  
Rudolf Kaul ◽  
Michael Shaw
Keyword(s):  
Methylene Blue ◽  
Redox System ◽  
Platinum Electrodes ◽  
Anaerobic Conditions ◽  
Mature Leaves ◽  
Reduction Potentials ◽  
Oxidation Reduction ◽  
Wheat Leaf ◽  
Steady Level ◽  
New System

Extracts from primary leaves of Little Club wheat, prepared under anaerobic conditions, gave oxidation–reduction potentials in the range of −180 mv to −140 mv at pH 6 when measured potentiometrically with prepolarized platinum electrodes. These poorly poised potentials are believed to represent a flavin system. By mixing mediators (e.g. methylene blue and riboflavin) with the extracts stable average potentials were achieved. These ranged from −70 to +70 mv. Coleoptiles and very young primary leaves exhibited relatively low average potentials, which climbed to a steady level in 8 to 10 days after sowing. This change was accompanied by a quantitative shift between three poising systems found in the leaves by redox titrations. The results suggested that ascorbic acid becomes the dominating redox system in extracts from mature leaves. At senescence, indicated by yellowing, a new system dominates the redox background. This exhibited quinonic properties.

scholarly journals Studies on the Oxidation-Reduction Potentials of Heme Proteins

1965 ◽  
Vol 240 (8) ◽  
pp. 3317-3324
Author(s):  
Maurizio Brunori ◽  
Jeffries Wyman ◽  
Eraldo Antonini ◽  
Alessandro Rossi-Fanelli
Keyword(s):  
Heme Proteins ◽  
Reduction Potentials ◽  
Oxidation Reduction
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