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.

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.

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.

scholarly journals Characterization and phenotypic control of the cytochrome content of Escherichia coli

1979 ◽  
Vol 182 (2) ◽  
pp. 465-472 ◽  
Author(s):  
Graeme A. Reid ◽  
W. John Ingledew
Keyword(s):  
Escherichia Coli ◽  
Electron Transport ◽  
Cytochrome B ◽  
Terminal Electron Acceptor ◽  
E Coli ◽  
Reduction Potentials ◽  
Electrode Potentials ◽  
Point Potential ◽  
Oxidation Reduction ◽  
Cytochrome D

1. Electron-transport particles derived from Escherichia coli grown aerobically contain three b-type cytochromes with mid-point oxidation–reduction potentials at pH7 of +260mV, +80mV and −50mV, with n=1 for each. The variation of these values with pH was determined. 2. E. coli develops a different set of b-type cytochromes when grown anaerobically on glycerol with fumarate or nitrate as terminal electron acceptor. Electron-transport particles of fumarate-grown cells contain b-type cytochromes with mid-point potentials at pH7 of +140mV and +250mV (n=1). These two cytochromes are also present in cells grown with nitrate as terminal acceptor, where an additional cytochrome b with a mid-point potential of +10mV (n=1) is developed. 3. The wavelengths of the α-absorption-band maxima of the b-type cytochromes at 77K were: (a) for aerobically grown cells, cytochrome b (Em7 +260mV), 556nm and 563nm, cytochrome b (Em7 +80mV), 556nm and cytochrome b (Em7−50mV), 558nm; (b) for anaerobically grown cells, cytochrome b (Em7 +250mV), 558nm, cytochrome b (Em7 +40mV), 555nm and cytochrome b (Em7 +10mV), 556nm. 4. Cytochrome d was found to have a mid-point potential at pH7 of +280mV (n=1). 5. Cytochrome a1 was resolved as two components of equal magnitude with mid-point potentials of +260mV and +160mV (n=1). 6. Redox titrations performed in the presence of CO showed that one of the b-type cytochromes in the aerobically grown cultures was reduced, even at the upper limits of our range of electrode potentials (above +400mV). Cytochrome d was also not oxidizable in the presence of CO. Neither of the cytochromes a1 was affected by the presence of CO.

scholarly journals Detection of cytochrome b+50 in membranes of Rhodospirillum rubrum isolated from aerobically and phototrophically grown cells

1980 ◽  
Vol 186 (2) ◽  
pp. 453-459 ◽  
Author(s):  
R A Niederman ◽  
C N Hunter ◽  
D E Mallon ◽  
O T Jones
Keyword(s):  
Cytochrome B ◽  
Rhodospirillum Rubrum ◽  
Electron Flow ◽  
Computer Assisted ◽  
Difference Spectra ◽  
Reduction Potentials ◽  
Oxidation Reduction ◽  
Assisted Analysis ◽  
Electron Equivalent ◽  
Three Components

1. Dark equilibrium potentiometric titrations were conducted on membranes purified from Rhodospirillum rubrum in an effort to identify b-type cytochrome components reported in other Rhodospirillaceae. In preparations from aerobically grown cells virtually devoid of bacteriochlorophyll a, three components were observed at 560-540 nm. Their oxidation-reduction midpoint potentials assigned by computer-assisted analysis were +195, +50 and −110 mV at pH 7.0; each of these fitted closely to theoretical single-electron equivalent curves. 2. In chromatophores from phototrophically grown carotenoidless mutant G-9, three components were also observed with E0' +190, +50 and −90mV. 3. The alpha-band of the +50mV component exhibited an absorption maximum near 560nm in difference spectra obtained at fixed oxidation-reduction potentials. 4. This component could be demonstrated most readily in purified membrane preparations and may have been obscured in previous studies by residual cytochrome c'. 5. This is the first definitive report of cytochrome b+50 in membranes from Rs. rubrum and aligns this bacterium with other Rhodospirillaceae in which this component functions in light-driven cyclic electron flow.

scholarly journals Oxidation–reduction potentials of molybdenum and iron–sulphur centres in nitrate reductase from Escherichia coli

1979 ◽  
Vol 177 (2) ◽  
pp. 757-759 ◽  
Author(s):  
S P Vincent
Keyword(s):  
Escherichia Coli ◽  
Nitrate Reductase ◽  
Escherichia Coli K12 ◽  
Reduction Potentials ◽  
Oxidation Reduction

The potentials of the couples Mo(IV)–(Mo(V) and Mo(V)–Mo(VI) in nitrate reductase from Escherichia coli K12 were measured as + 180 mV and + 220 mV respectively at pH 7.14. The potentials associated with two other e.p.r. signals, believed to be due to iron–sulphur centres, were measured as + 50 mV and + 80 mV.

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).

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