scholarly journals Studies on partially reduced mammalian cytochrome oxidase. Reactions with carbon monoxide and oxygen

1974 ◽  
Vol 137 (2) ◽  
pp. 205-215 ◽  
Author(s):  
Colin Greenwood ◽  
Michael T. Wilson ◽  
Maurizio Brunori
Keyword(s):  
Cytochrome Oxidase ◽  
Redox State ◽  
Mixed Valence ◽  
Order Rate Constant ◽  
Low Oxygen ◽  
Difference Spectra ◽  
Ferrocytochrome C ◽  
Kinetics Of ◽  
Enzyme Species ◽  
Binding Behaviour

A number of methods were used to prepare a species of mammalian cytochrome oxidase (EC 1.9.3.1, ferrocytochrome c–oxygen oxidoreductase) in which only cytochrome a3 is reduced and in combination with CO. The kinetics of CO binding by cytochrome a32+ in this species is significantly different from that exhibited by cytochrome a32+ in the fully reduced enzyme. The second-order rate constant for combination was 5X104m−1·s−1 and the ‘off’ constant was 3X10−2s−1. The kinetic difference spectra cytochrome a32+–cytochrome a32+–CO reveal further differences between the mixed-valence and the fully reduced enzyme. The reaction between cytochrome a32+ and oxygen in the mixed-valence species was followed in flow–flash experiments and reveals a fast, oxygen-dependent (8X107m−1·s−1 at low oxygen) rate followed by a slow process, whose rate is independent of oxygen but whose amplitude is dependent on [O2]. The fast oxygen-dependent reaction yields as the first product the so-called ‘oxygenated’ enzyme. We conclude from these experiments that the ligand-binding behaviour of cytochrome a3 depends on the redox state of its partners, a fact which represents clear evidence for site–site interaction in this enzyme. The fact that oxygen reacts rapidly with this enzyme species in which only one component, namely cytochrome a3, is reduced represents clear and unequivocal evidence that this is indeed the O2-binding site in cytochrome oxidase and may indicate that reduction of oxygen can proceed via single electron steps.

scholarly journals Spectroscopic forms of carbonmonoxi-cytochrome oxidase

1979 ◽  
Vol 183 (2) ◽  
pp. 375-379 ◽  
Author(s):  
K de Fonseka ◽  
B Chance
Keyword(s):  
Low Temperature ◽  
Cytochrome Oxidase ◽  
Systematic Study ◽  
Residual Effect ◽  
Difference Spectra ◽  
Temperature Recording ◽  
Devitrification Process ◽  
Kinetics Of

A systematic study of the errors of low-temperature recording of kinetics of the cytochrome oxidase-CO reaction had identified the classic devitrification process of Keilin & Hartree [(1950) Nature (London)165, 504-505]. The methodology described here minimizes this effect, and the computation methods afford appropriate ways of detecting a residual effect. Thus it has been possible to identify that absorption difference spectra and kinetics of the reaction of fully reduced or half-reduced cytochrome oxidase with CO indicate only one spectroscopic form of the respective carbonmonoxi-cytochrome oxidase.

scholarly journals Low-temperature kinetics of the reaction of oxygen and solubilized cytochrome oxidase

1978 ◽  
Vol 171 (3) ◽  
pp. 787-798 ◽  
Author(s):  
B Chance ◽  
C Saronio ◽  
J S Leigh ◽  
W J Ingledew ◽  
T E King
Keyword(s):  
Cytochrome Oxidase ◽  
Mixed Valence ◽  
Similar Species ◽  
Absorption Bands ◽  
Compound C ◽  
Valence States ◽  
Membrane Bound ◽  
Peroxy Compounds ◽  
Band Characteristic ◽  
Kinetics Of

The reaction of solubilized cytochrome oxidase in the fully reduced state with O2 at low temperatures reveals components with characteristics similar to those observed with the membrane-bound oxidase, namely compounds A and B, which are proposed to be ‘oxy’ and ‘peroxy’ compounds respectively. Similar species are identified in both solubilized and membrane-bound oxidases; the reaction velocity constant for the reation with O2 and the dissociation constant are decreased 2-3-fold in the solubilied preparation as compared with the membrane-bound species, owing to decreased reactivity towards O2 in the former. The oxidase prepared in the mixed-valence state shows the distinctive absorption band characteristic of compound C, identified in the membrane-bound oxidase. The assignment of the alpha, beta, gamma and near-i.r. absorption bands to possible valence states of these compounds is made.

scholarly journals Chromous ion reduction of mammalian cytochrome oxidase and some of its derivatives

1977 ◽  
Vol 165 (2) ◽  
pp. 413-416 ◽  
Author(s):  
C Greenwood ◽  
T Brittain ◽  
M Brunori ◽  
M T Wilson
Keyword(s):  
Mixed Valence ◽  
Slow Phase ◽  
High Concentration ◽  
Difference Spectra ◽  
Rapid Phase ◽  
Fast Phase ◽  
Two Phases ◽  
Rate Limit ◽  
Kinetics Of ◽  
Inhibited Enzyme

The reduction of cytochrome c oxidase by Cr2+, followed by means of stopped-flow spectrophotometry, exhibits two phases: the faster Cr2+-concentration-dependent reaction has an initial rate constant of 1.1 × 10(4)M-1-S-1, but reaches a rate limit at high concentration of reductant; the slower phase is concentration-independent with a rate of 0.3S-1. The activation energies of the fast and the slow processes are 35 and 71 kJ/mol respectively. The reduction kinetics of the mixed-valence CO complex and the cyanide-inhibited enzyme were compared with those of the fully oxidized forms: both the liganded species have a fast phase identical with that found in the oxidized oxidase. A comparison of the kinetic difference spectra obtained for the fast phase of reduction of oxidized oxidase with those obtained on reduction of the liganded species suggests that the rapid phase arises from the reduction ofhaem a, and the slow phase from the reduction of haem a3.

scholarly journals Characterization of the intermediates in the reaction of mixed-valence state soluble cytochrome oxidase with oxygen at low temperatures by optical and electron-paramagnetic-resonance spectroscopy

1980 ◽  
Vol 185 (1) ◽  
pp. 155-167 ◽  
Author(s):  
G M Clore ◽  
L E Andréasson ◽  
B Karlsson ◽  
R Aasa ◽  
B G Malmström
Keyword(s):  
Cytochrome Oxidase ◽  
Valence State ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Mixed Valence ◽  
Spectroscopic Properties ◽  
Resonance Spectroscopy ◽  
Difference Spectra ◽  
Paramagnetic Resonance ◽  
Mixed Valence State ◽  
The Difference

The reaction of soluble mixed-valence-state (a3+CuA2+.CuB+A32+) cytochrome oxidase with O2 at low temperature was studied by optical and e.p.r. spectroscopy. The existence of three intermediates [Clore & Chance (1978) Biochem. J. 173, 799-8101] was confirmed. From the e.p.r data it is clear that cytochrome a and CuA remain in the low-spin ferric and cupric states respectively throughout the reaction. No e.p.r. signals attributable to cytochrome a3 or CuB were seen in the intermediates. The difference spectra (intermediates minus unliganded mixed-valence-state cytochrome oxidase) and absolute spectra of the three intermediates were obtained. The chemcal nature of the three intermediates is discussed in terms of their spectroscopic properties. A catalytic cycle for cytochrome oxidase is proposed.

scholarly journals The oxidation of Pseudomonas cytochrome c-551 oxidase by potassium ferricyanide

1978 ◽  
Vol 173 (2) ◽  
pp. 681-690 ◽  
Author(s):  
D Barber ◽  
S R Parr ◽  
C Greenwood
Keyword(s):  
Cytochrome Oxidase ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Potassium Ferricyanide ◽  
Second Order ◽  
Difference Spectra ◽  
Bimolecular Reactions ◽  
Order Rate ◽  
N2 Atmosphere ◽  
Co Dissociation

Stopped-flow kinetics were made of the reaction between ascorbate-reduced Pseudomonas cytochrome oxidase and potassium ferricyanide under both N2 and CO atmospheres. Under N2 three kinetic processes were observed, two being dependent on ferricyanide concentration, with second-order rate constants of 9.6×10(4)M-1.s-1 and 1.5×10(4)M-1.s-1, whereas the other was concentration-independent, with a first-order rate constant of 0.17 +/- 0.03s-1. Measurements of their kinetic difference spectra have allowed the fastest and second-fastest phases of the reaction to be assigned to direct bimolecular reactions of ferricyanide with the haem c and haem d, moieties of the enzyme respectively. Under CO, the second-order rate constant for the reaction of the haem c was, at 1.3×10(5)M-1.s-1, slightly enhanced over the rate in a N2 atmosphere, but the reaction velocity of the haem d1 component was greatly decreased, being apparently limited to that of the rates of CO dissociation from the molecule (0.15s-1 and 0.03s-1). The results are compared with those obtained during a previous study of the reaction of reduced Pseudomonas cytochrome oxidase with oxidized azurin.

Defects in oxide overlayers at nickel single-crystal surfaces

1985 ◽  
Vol 399 (1816) ◽  
pp. 167-179 ◽  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Relative Proportion ◽  
Mixed Valence ◽  
Binding Energies ◽  
Low Oxygen ◽  
Nickel Oxides ◽  
Difference Spectra ◽  
Simultaneous Generation ◽  
Valence States ◽  
Oxygen Interaction

The chemisorption of oxygen at Ni(100) and Ni(210) surfaces has been studied by X -ray photoelectron spectroscopy in the temperature range 77-300 K. O(1s) spectra distinguished between the formation of O - and O 2- species while Ni(2p) spectra revealed the formation of Ni 2+ and Ni 3+ states. The binding energies of the latter are 854.7 and 856 eV respectively. These values were established by the generation of difference spectra in the Ni(2p) spectral region and assignments confirmed by studies of bulk nickel oxides of different stoichiometry. There were two distinct régimes of oxygen interaction; for low oxygen coverages, θ < 0.6, there was no evidence for the higher oxidation states (Ni 2+ or Ni 3+ ). For θ > 0.6 the Ni(2p) difference spectra indicated that both states were formed, their relative proportions being dependent on temperature and coverage. It is suggested that the initial stage of oxygen chemisorption involves only the Ni(4s4p) band while the Ni(3d) electrons participate in oxide formation, which is reflected by the emergence of Ni 2+ and Ni 3+ states. Ni (L 2, 3 M 4, 5 M 4, 5 ) Auger spectra and also recent theoretical work support this conclusion. The mixed valence states, Ni 2+ and Ni 3+ , are a characteristic feature not only of oxygen interaction with Ni(210) and Ni(100) at low temperature but also of the surface of bulk nickel oxides. The latter unexpectedly exhibit a high relative proportion of Ni 3+ states. It is suggested that Ni 3+ is formed in a surface redox reaction from Ni 2+ with the simultaneous generation of O - . Angular dependent studies confirm that the Ni 3+ and O - species are at the surface relative to Ni 2+ and O 2- .

scholarly journals Characterization of the intermediates in the reaction of membrane-bound mixed-valence-state cytochrome oxidase with oxygen at low temperatures by optical spectroscopy in the visible region

1980 ◽  
Vol 187 (3) ◽  
pp. 617-622 ◽  
Author(s):  
G M Clore
Keyword(s):  
Cytochrome Oxidase ◽  
Optical Spectroscopy ◽  
Valence State ◽  
Mixed Valence ◽  
Visible Region ◽  
Difference Spectrum ◽  
Difference Spectra ◽  
Mixed Valence State ◽  
Membrane Bound ◽  
The Difference

The ‘pure’ difference spectra of the three species, IM, IIM and IIIM, formed in the low-temperature reaction of membrane-bound mixed-valence-state cytochrome oxidase with O2 relative to unliganded membrane-bound mixed-valence-state cytochrome oxidase were characterized by optical spectroscopy in the visible region. The difference spectrum of species IM was characterized by a peak at 590 nm and a trough at 608 nm, that of species IIM by a peak at 606 nm, and that of species IIIM by a peak at 610 nm. A comparison with the difference spectra of species IIM and IIIM obtained with soluble cytochrome oxidase [Clore, Andréasson, Karlsson, Aasa & Malmström (1980) Biochem. J. 185, 155-167] revealed small but significant differences in the peak positions and bandwidths of the 605-610 nm absorption band.

Regulation of cytochrome oxidase redox state during umbilical cord occlusion in preterm fetal sheep

2007 ◽  
Vol 292 (4) ◽  
pp. R1569-R1576 ◽  
Author(s):  
Laura Bennet ◽  
Vincent Roelfsema ◽  
Justin M. Dean ◽  
Guido Wassink ◽  
Gordon G. Power ◽  
...  
Keyword(s):  
Cytochrome Oxidase ◽  
Umbilical Cord ◽  
Redox State ◽  
Cerebral Oxygenation ◽  
Cerebral Metabolism ◽  
Electron Flow ◽  
Initial Response ◽  
Severe Hypoxia ◽  
Fetal Sheep ◽  
Severe Hypotension

The preterm fetus is capable of surviving prolonged periods of severe hypoxia without neural injury for much longer than at term. To evaluate the hypothesis that regulated suppression of brain metabolism contributes to this remarkable tolerance, we assessed changes in the redox state of cytochrome oxidase (CytOx) relative to cerebral heat production, and cytotoxic edema measured using cerebral impedance, during 25 min of complete umbilical cord occlusion or sham occlusion in fetal sheep at 0.7 gestation. Occlusion was followed by rapid, profound reduction in relative cerebral oxygenation and EEG intensity and an immediate increase in oxidized CytOx, indicating a reduction in electron flow down the mitochondrial electron transfer chain. Confirming rapid suppression of cerebral metabolism there was a loss of the temperature difference between parietal cortex and body at a time when carotid blood flow was maintained at control values. As occlusion continued, severe hypotension/hypoperfusion developed, with a further increase in CytOx levels to a plateau between 8 and 13 min and a progressive rise in cerebral impedance. In conclusion, these data strongly suggest active regulation of cerebral metabolism during the initial response to severe hypoxia, which may help to protect the immature brain from injury.

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