scholarly journals An active cytochrome c oxidase that has no tightly bound cardiolipin

1983 ◽  
Vol 209 (3) ◽  
pp. 901-903 ◽  
Author(s):  
W F Al-Tai ◽  
M G Jones ◽  
K Rashid ◽  
M T Wilson
Keyword(s):  
Steady State ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Squalus Acanthias ◽  
Submitochondrial Particles

Bovine and dogfish (Squalus acanthias) heart submitochondrial particles and cytochrome c oxidase (EC 1.9.3.1) were prepared. Biphasic Eadie-Hofstee plots from steady-state polarographic assays were obtained for both species. Phospholipid analyses indicated that cardiolipin was absent from this active dogfish enzyme.

Sulphide as an inhibitor and electron donor for the cytochrome c oxidase system

1982 ◽  
Vol 60 (6) ◽  
pp. 613-623 ◽  
Author(s):  
P. Nicholls ◽  
J.-K. Kim
Keyword(s):  
Cytochrome C ◽  
Oxygen Uptake ◽  
Cytochrome C Oxidase ◽  
Submitochondrial Particles ◽  
Inhibitory Interaction ◽  
Cytochromes C ◽  
Subsequent Step ◽  
Oxidase Enzyme ◽  
Rapid Reaction ◽  
The One

Anomalies both kinetic and equilibrium in nature are described for the inhibition of cytochrome c oxidase activity by sulphide in the isolated enzyme and in submitochondrial particles. These anomalies are related to the involvement of more than 1 mol of sulphide in the blockage of one cytochrome aa3 centre. Sulphide reduces resting cytochrome a3, a reaction that results in oxygen uptake and the loss of a sulphide molecule. Sulphide can also reduce cytochromes c and a; in the former case, a part of the one-equivalent oxidation product, presumed to be the SH∙ radical, reacts with oxygen. Such oxygen uptake is also seen under aerobic conditions when ferricyanide reacts with sulphide. Three phases are identified in the inhibitory interaction of sulphide with the cytochrome c oxidase enzyme itself: an initial rapid reaction involving sulphide oxidation, oxygen uptake, and conversion of cytochrome aa3 into the low-spin "oxyferri" form; a subsequent step in which sulphide reduces cytochrome a; and the final inhibitory step in which a third molecule of sulphide binds the a3 iron centre in the cytochrome [Formula: see text] (oxy) species to give cytochrome [Formula: see text]. The initial events parallel some of the events in the interaction of the cytochrome c – cytochrome aa3 system with monothiols; the final inhibitory event resembles that with cyanide.

Kinetics of the cytochrome c oxidase and reductase reactions in energized and de-energized mitochondria

1977 ◽  
Vol 55 (7) ◽  
pp. 706-713 ◽  
Author(s):  
Lars Chr. Petersen ◽  
Hans Degn ◽  
Peter Nicholls
Keyword(s):  
Steady State ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Oxygen Concentration ◽  
Respiration Rate ◽  
Redox State ◽  
Rat Liver Mitochondria ◽  
Excess Oxygen ◽  
Succinate Oxidation ◽  
State Reduction

1. Coupled, cytochrome-c-depleted ('stripped') rat liver mitochondria reducing oxygen in the presence of exogenous cytochrome c, with succinate or ascorbate as substrates, show marked declines in the steady-state reduction of cytochrome c in excess oxygen on addition of uncouplers. Calculated ratios of maximal turnover in the uncoupled state and in the energized state for the cytochrome c oxidase (EC 1.9.3.1) reaction lie between 3 and 6, as obtained with reconstituted oxidase-containing vesicles. The succinate-cytochrome c reductase activity in such mitochondria shows a smaller response to uncoupler than that of the oxidase.2. The respiration rates of uncoupled mitochondria oxidizing ascorbate in the presence of added cytochrome c follow a Michaelis–Menten relationship with respect to oxygen concentration, in accordance with the pattern found previously with the solubilized oxidase. But succinate oxidation tends to give nonlinear concave-upward double-reciprocal plots of respiration rate against oxygen concentration, in accordance with the pattern found previously with intact uncoupled mitochondria.3. From simultaneous measurements of cytochrome c steady-state reduction, respiration rate, and oxygen concentration during succinate oxidation under uncoupled conditions it is found that at full reduction of cytochrome c, apparent Km for oxygen is 0.9 μM and the maximal oxidase (aa3) turnover is 400 s−1 (pH 7.4, 30 °C).4. The redox state of cytochrome c in uncoupled systems reflects a simple steady state; the redox state of cytochrome c in energized systems tends towards an equilibrium condition with the terminal cytochrome a3, whose apparent potential under these conditions is more negative than that of cytochrome c.

scholarly journals Titration and steady-state behaviour of the 830 nm chromophore in cytochrome c oxidase

1982 ◽  
Vol 203 (3) ◽  
pp. 541-549 ◽  
Author(s):  
P Nicholls ◽  
G A Chanady
Keyword(s):  
Steady State ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Lag Phase ◽  
State Reduction ◽  
Cytochrome Aa3 ◽  
System A ◽  
Reducing Equivalent ◽  
State Behaviour ◽  
Copper Excess

Titration of cyanide-incubated cytochrome c oxidase (ox heart cytochrome aa3) with ferrocytochrome c or with NNN'N'-tetramethyl-p-phenylenediamine initially introduces two reducing equivalents per mol of cytochrome aa3. The first equivalent reduces the cytochrome a haem iron; the second reducing equivalent is not associated with reduction of the 830 nm chromophores (e.p.r.-detectable copper) but is probably required for reduction of the e.p.r.-undetectable copper. Excess reductant introduces a third reducing equivalent into the cyanide complex of cytochrome aa3. During steady-state respiration in the presence of cytochrome c and ascorbate, the 830 nm chromophore is almost completely oxidized. It is reduced more slowly than cytochrome a on anaerobiosis. In the presence of formate or azide, some reduction at 830 nm can be seen in the steady state; in an oxygen-pulsed system, a decrease in steady-state reduction of cytochromes c and a is associated with ab increased reduction of the 830 nm species. In the formate-inhibited system the reduction of a3 on anaerobiosis shows a lag phase, the duration of which corresponds to the time taken for the 830 nm species to be reduced. It is concluded that the e.p.r.-undetectable copper (CuD) is reduced early in the reaction sequence, whereas the detectable copper (CUD) is reduced late. The latter species is probably that responsible for reduction of the cytochrome a3 haem. The magnetic association between undetectable copper and the a3 haem may not imply capability for electron transfer, which occurs more readily between cytochrome a3 and the 830 nm species.

scholarly journals S11. 10 Steady state redox interactions of cytochrome c oxidase

2008 ◽  
Vol 1777 ◽  
pp. S67
Author(s):  
Maria G. Mason ◽  
Peter Nichols ◽  
Chris E. Cooper
Keyword(s):  
Steady State ◽  
Cytochrome C ◽  
Cytochrome C Oxidase

The orientation of a heme of cytochrome c oxidase in submitochondrial particles

1978 ◽  
Vol 502 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Haywood Blum ◽  
H.J. Harmon ◽  
J.S. Leigh ◽  
J.C. Salerno ◽  
Britton Chance
Keyword(s):  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Submitochondrial Particles

Routes of electron transfer in beef heart cytochrome c oxidase: is there a unique pathway used by all reductants?

1992 ◽  
Vol 70 (5) ◽  
pp. 301-308 ◽  
Author(s):  
M. Crinson ◽  
P. Nicholls
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Reduction Rate ◽  
Artificial Substrates ◽  
Intramolecular Electron Transfer ◽  
State Reduction ◽  
Hydrogen Donors ◽  
Slow Turnover

Cytochrome c oxidase oxidizes several hydrogen donors, including TMPD (N,N,N′,N′-tetramethyl-p-phenylenediamine) and DMPT (2-amino-6,7-dimethyl-5,6,7,8-tetrahydropterine), in the absence of the physiological substrate cytochrome c. Maximal enzyme turnovers with TMPD and DMPT alone are rather less than with cytochrome c, but much greater than previously reported if extrapolated to high reductant levels and (or) to 100% reduction of cytochrome a in the steady state. The presence of cytochrome c is, therefore, not necessary for substantial intramolecular electron transfer to occur in the oxidase. A direct bimolecular reduction of cytochrome a by TMPD is sufficient to account for the turnover of the enzyme. CuA may not be an essential component of the TMPD oxidase pathway. DMPT oxidation seems to occur more rapidly than the DMPT – cytochrome a reduction rate and may therefore imply mediation of CuA. Both "resting" and "pulsed" oxidases contain rapid-turnover and slow-turnover species, as determined by aerobic steady-state reduction of cytochrome a by TMPD. Only the "rapid" fraction (≈70% of the total with resting and ≈85% of the total with pulsed) is involved in turnover. We conclude that electron transfer to the a3CuB binuclear centre can occur either from cytochrome a or CuA, depending upon the redox state of the binuclear centre. Under steady-state conditions, cytochrome a and CuA may not always be in rapid equilibrium. Rapid enzyme turnover by either natural or artificial substrates may require reduction of both and two pathways of electron transfer to the a3CuB centre.Key words: cytochrome c oxidase, cytochrome a, respiration, cyanide, stopped flow.

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