Steady-state transcript levels of cytochrome c oxidase genes during human myogenesis indicate subunit switching of subunit VIa and co-expression of subunit VIIa isoforms

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.

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Steady-state levels of subunits of respiratory chain enzymes: clues to the primary genetic defect in cytochrome c oxidase deficiencies

Genetics Research ◽

10.1017/s0016672398433305 ◽

1998 ◽

Vol 72 (1) ◽

pp. 59-72

Author(s):

SION WILLIAMS ◽

J. W. TAANMAN ◽

H. R. SCHOLTE ◽

A. SCHAPIRA

Keyword(s):

Steady State ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Respiratory Chain ◽

Genetic Defect ◽

Steady State Levels

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

Biochemical Journal ◽

10.1042/bj2030541 ◽

1982 ◽

Vol 203 (3) ◽

pp. 541-549 ◽

Cited By ~ 18

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.

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S11. 10 Steady state redox interactions of cytochrome c oxidase

Biochimica et Biophysica Acta (BBA) - Bioenergetics ◽

10.1016/j.bbabio.2008.05.265 ◽

2008 ◽

Vol 1777 ◽

pp. S67

Author(s):

Maria G. Mason ◽

Peter Nichols ◽

Chris E. Cooper

Keyword(s):

Steady State ◽

Cytochrome C ◽

Cytochrome C Oxidase

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Electron-transport-driven proton pumps display nonhyperbolic kinetics: Simulation of the steady-state kinetics of cytochrome c oxidase

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.83.12.4282 ◽

1986 ◽

Vol 83 (12) ◽

pp. 4282-4286 ◽

Cited By ~ 38

Author(s):

P. Brzezinski ◽

B. G. Malmstrom

Keyword(s):

Steady State ◽

Electron Transport ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Proton Pumps ◽

Steady State Kinetics ◽

Kinetics Simulation ◽

Kinetics Of

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

Biochemistry and Cell Biology ◽

10.1139/o92-047 ◽

1992 ◽

Vol 70 (5) ◽

pp. 301-308 ◽

Cited By ~ 8

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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