Mitochondrial oxygen affinity, respiratory flux control and excess capacity of cytochrome c oxidase.

The oxygen affinity of the enzyme system involved in mitochondrial respiration indicates, in relation to intracellular oxygen levels and interpreted with the aid of flux control analysis, a significant role of oxygen supply in limiting maximum exercise. This implies that the flux control coefficient of mitochondria is not excessively high, based on a capacity of mitochondrial oxygen consumption that is slightly higher than the capacity for oxygen supply through the respiratory cascade. Close matching of the capacities and distribution of flux control is consistent with the concept of symmorphosis. Within the respiratory chain, however, the large excess capacity of cytochrome c oxidase, COX, appears to be inconsistent with the economic design of the respiratory cascade. To address this apparent discrepancy, we used three model systems: cultured endothelial cells and mitochondria isolated from heart and liver. Intracellular oxygen gradients increase with oxygen flux, explaining part of the observed decrease in oxygen affinity with increasing metabolic rate in cells. In addition, mitochondrial oxygen affinities decrease from the resting to the active state. The oxygen affinity in the active ADP-stimulated state is higher in mitochondria from heart than in those from liver, in direct relationship to the higher excess capacity of COX in heart. This yields, in turn, a lower turnover rate of COX even at maximum flux through the respiratory chain, which is necessary to prevent a large decrease in oxygen affinity in the active state. Up-regulation of oxygen affinity provides a functional explanation of the excess capacity of COX. The concept of symmorphosis, a matching of capacities in the respiratory cascade, is therefore complemented by 'synkinetic' considerations on optimum enzyme ratios in the respiratory chain. Accordingly, enzymatic capacities are matched in terms of optimum ratios, rather than equal levels, to meet the specific kinetic and thermodynamic demands set by the low-oxygen environment in the cell.

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Mitochondrial respiration at low levels of oxygen and cytochrome c

Biochemical Society Transactions ◽

10.1042/bst0300252 ◽

2002 ◽

Vol 30 (2) ◽

pp. 252-258 ◽

Cited By ~ 94

Author(s):

E. Gnaiger ◽

A. V. Kuznetsov

Keyword(s):

Cytochrome C ◽

Cytochrome C Oxidase ◽

Respiratory Chain ◽

Isolated Heart ◽

Hyperbolic Function ◽

Excess Capacity ◽

Hypoxic Conditions ◽

Substrate Limitation ◽

Oxygen Conditions ◽

Low Levels

In the intracellular microenvironment of active muscle tissue, high rates of respiration are maintained at near-limiting oxygen concentrations. The respiration of isolated heart mitochondria is a hyperbolic function of oxygen concentration and half-maximal rates were obtained at 0.4 and 0.7 μM O2 with substrates for the respiratory chain (succinate) and cytochrome c oxidase [N, N, N, N', N'-tetramethyl-p-phenylenediamine dihydrochloride (TMPD) + ascorbate] respectively at 30 °C and with maximum ADP stimulation (State 3). The respiratory response of cytochrome c-depleted mitoplasts to external cytochrome c was biphasic with TMPD, but showed a monophasic hyperbolic function with succinate. Half-maximal stimulation of respiration was obtained at 0.4 μM cytochrome c, which was nearly identical to the high-affinity K'm for cytochrome c of cytochrome c oxidase supplied with TMPD. The capacity of cytochrome c oxidase in the presence of TMPD was 2-fold higher than the capacity of the respiratory chain with succinate, measured at environmental normoxic levels. This apparent excess capacity, however, is significantly decreased under physiological intracellular oxygen conditions and declines steeply under hypoxic conditions. Similarly, the excess capacity of cytochrome c oxidase declines with progressive cytochrome c depletion. The flux control coefficient of cytochrome c oxidase, therefore, increases as a function of substrate limitation of oxygen and cytochrome c, which suggests a direct functional role for the apparent excess capacity of cytochrome c oxidase in hypoxia and under conditions of intracellular accumulation of cytochrome c after its release from mitochondria.

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Control by cytochrome c oxidase of the cellular oxidative phosphorylation system depends on the mitochondrial energy state

Biochemical Journal ◽

10.1042/bj20060077 ◽

2006 ◽

Vol 396 (3) ◽

pp. 573-583 ◽

Cited By ~ 63

Author(s):

Claudia Piccoli ◽

Rosella Scrima ◽

Domenico Boffoli ◽

Nazzareno Capitanio

Keyword(s):

Cytochrome C ◽

Oxidative Phosphorylation ◽

Cytochrome C Oxidase ◽

Energy State ◽

Exercise Intolerance ◽

Regulatory Function ◽

Control Analysis ◽

Intact Cells ◽

Flux Control ◽

The Impact

Recent measurements of the flux control exerted by cytochrome c oxidase on the respiratory activity in intact cells have led to a re-appraisal of its regulatory function. We have further extended this in vivo study in the framework of the Metabolic Control Analysis and evaluated the impact of the mitochondrial transmembrane electrochemical potential (ΔμH+) on the control strength of the oxidase. The results indicate that, under conditions mimicking the mitochondrial State 4 of respiration, both the flux control coefficient and the threshold value of cytochrome oxidase are modified with respect to the uncoupled condition. The results obtained are consistent with a model based on changes in the assembly state of the oxidative phosphorylation enzyme complexes and possible implications in the understanding of exercise-intolerance of human neuromuscular degenerative diseases are discussed.

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Regulation of Cytochrome c Oxidase by Natural Compounds Resveratrol, (–)-Epicatechin, and Betaine

Cells ◽

10.3390/cells10061346 ◽

2021 ◽

Vol 10 (6) ◽

pp. 1346

Author(s):

Icksoo Lee

Keyword(s):

Cytochrome C ◽

Cytochrome C Oxidase ◽

Model Systems ◽

Health Improvement ◽

Published Data ◽

Mitochondrial Electron Transport Chain ◽

Naturally Occurring ◽

Transport Chain ◽

Wide Range ◽

Experimental Model Systems

Numerous naturally occurring molecules have been studied for their beneficial health effects. Many compounds have received considerable attention for their potential medical uses. Among them, several substances have been found to improve mitochondrial function. This review focuses on resveratrol, (–)-epicatechin, and betaine and summarizes the published data pertaining to their effects on cytochrome c oxidase (COX) which is the terminal enzyme of the mitochondrial electron transport chain and is considered to play an important role in the regulation of mitochondrial respiration. In a variety of experimental model systems, these compounds have been shown to improve mitochondrial biogenesis in addition to increased COX amount and/or its enzymatic activity. Given that they are inexpensive, safe in a wide range of concentrations, and effectively improve mitochondrial and COX function, these compounds could be attractive enough for possible therapeutic or health improvement strategies.

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Heteroplasmic Point Mutations of Mitochondrial DNA Affecting Subunit I of Cytochrome c Oxidase in Two Patients With Acquired Idiopathic Sideroblastic Anemia

Blood ◽

10.1182/blood.v90.12.4961.4961_4961_4972 ◽

1997 ◽

Vol 90 (12) ◽

pp. 4961-4972 ◽

Cited By ~ 1

Author(s):

Norbert Gattermann ◽

Stefan Retzlaff ◽

Yan-Ling Wang ◽

Götz Hofhaus ◽

Jürgen Heinisch ◽

...

Keyword(s):

Bone Marrow ◽

Mitochondrial Dna ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Respiratory Chain ◽

Ferric Iron ◽

Point Mutations ◽

Polymorphism Analysis ◽

Sideroblastic Anemia ◽

Wide Range

Mitochondrial iron overload in acquired idiopathic sideroblastic anemia (AISA) may be attributable to mutations of mitochondrial DNA (mtDNA), because these can cause respiratory chain dysfunction, thereby impairing reduction of ferric iron (Fe3+) to ferrous iron (Fe2+). The reduced form of iron is essential to the last step of mitochondrial heme biosynthesis. It is not yet understood to which part of the respiratory chain the reduction of ferric iron is linked. In two patients with AISA we identified point mutations of mtDNA affecting the same transmembrane helix within subunit I of cytochrome c oxidase (COX I; ie, complex IV of the respiratory chain). The mutations were detected by restriction fragment length polymorphism analysis and temperature gradient gel electrophoresis. One of the mutations involves a T → C transition in nucleotide position 6742, causing an amino acid change from methionine to threonine. The other mutation is a T → C transition at nt 6721, changing isoleucine to threonine. Both amino acids are highly conserved in a wide range of species. Both mutations are heteroplasmic, ie, they establish a mixture of normal and mutated mitochondrial genomes, which is typical of disorders of mtDNA. The mutations were present in bone marrow and whole blood samples, in isolated platelets, and in granulocytes, but appeared to be absent from T and B lymphocytes purified by immunomagnetic bead separation. They were not detected in buccal mucosa cells obtained by mouthwashes and in cultured skin fibroblasts examined in one of the patients. In both patients, this pattern of involvement suggests that the mtDNA mutation occurred in a self-renewing bone marrow stem cell with myeloid determination. Identification of two point mutations with very similar location suggests that cytochrome c oxidase plays an important role in the pathogenesis of AISA. COX may be the physiologic site of iron reduction and transport through the inner mitochondrial membrane.

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Cytochrome aa3 in facultatively aerobic and hyperthermophilic archaeon Pyrobaculum oguniense

Canadian Journal of Microbiology ◽

10.1139/w05-040 ◽

2005 ◽

Vol 51 (8) ◽

pp. 621-627 ◽

Cited By ~ 4

Author(s):

Takuro Nunoura ◽

Yoshihiko Sako ◽

Takayoshi Wakagi ◽

Aritsune Uchida

Keyword(s):

Oxygen Consumption ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Gene Product ◽

Respiratory Chain ◽

Oxidase Activity ◽

Terminal Oxidase ◽

Hyperthermophilic Archaeon ◽

Consumption Activity ◽

Copper Oxidase

We partially purified and characterized the cytochrome aa3 from the facultatively aerobic and hyperthermophilic archaeon Pyrobaculum oguniense. This cytochrome aa3 showed oxygen consumption activity with N, N, N′, N′-tetramethyl-1,4-phenylenediamine and ascorbate as substrates, and also displayed bovine cytochrome c oxidase activity. These enzymatic activities of cytochrome aa3 were inhibited by cyanide and azide. This cytochrome contained heme As, but not typical heme A. An analysis of trypsin-digested fragments indicated that 1 subunit of this cytochrome was identical to the gene product of subunit I of the SoxM-type heme – copper oxidase (poxC). This is the first report of a terminal oxidase in hyperthermophilic crenarchaeon belonging to the order Thermoproteales.Key words: aerobic respiratory chain, terminal oxidase, Archaea, hyperthermophile, Pyrobaculum.

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Effect of Deficiency of Cytochrome C Oxidase Assembly Peptide Cox17p on Mitochondrial Functions and Respiratory-Chain in Mice

Peptides: The Wave of the Future ◽

10.1007/978-94-010-0464-0_372 ◽

2001 ◽

pp. 795-796

Author(s):

Yoshinori Takahashi ◽

Koichiro Kako ◽

Hidenori Arai ◽

Akio Takehara ◽

Eisuke Munekata

Keyword(s):

Cytochrome C ◽

Cytochrome C Oxidase ◽

Respiratory Chain ◽

Mitochondrial Functions

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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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Heteroplasmic Point Mutations of Mitochondrial DNA Affecting Subunit I of Cytochrome c Oxidase in Two Patients With Acquired Idiopathic Sideroblastic Anemia

Blood ◽

10.1182/blood.v90.12.4961 ◽

1997 ◽

Vol 90 (12) ◽

pp. 4961-4972 ◽

Cited By ~ 120

Author(s):

Norbert Gattermann ◽

Stefan Retzlaff ◽

Yan-Ling Wang ◽

Götz Hofhaus ◽

Jürgen Heinisch ◽

...

Keyword(s):

Bone Marrow ◽

Mitochondrial Dna ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Respiratory Chain ◽

Ferric Iron ◽

Point Mutations ◽

Polymorphism Analysis ◽

Sideroblastic Anemia ◽

Wide Range

Abstract Mitochondrial iron overload in acquired idiopathic sideroblastic anemia (AISA) may be attributable to mutations of mitochondrial DNA (mtDNA), because these can cause respiratory chain dysfunction, thereby impairing reduction of ferric iron (Fe3+) to ferrous iron (Fe2+). The reduced form of iron is essential to the last step of mitochondrial heme biosynthesis. It is not yet understood to which part of the respiratory chain the reduction of ferric iron is linked. In two patients with AISA we identified point mutations of mtDNA affecting the same transmembrane helix within subunit I of cytochrome c oxidase (COX I; ie, complex IV of the respiratory chain). The mutations were detected by restriction fragment length polymorphism analysis and temperature gradient gel electrophoresis. One of the mutations involves a T → C transition in nucleotide position 6742, causing an amino acid change from methionine to threonine. The other mutation is a T → C transition at nt 6721, changing isoleucine to threonine. Both amino acids are highly conserved in a wide range of species. Both mutations are heteroplasmic, ie, they establish a mixture of normal and mutated mitochondrial genomes, which is typical of disorders of mtDNA. The mutations were present in bone marrow and whole blood samples, in isolated platelets, and in granulocytes, but appeared to be absent from T and B lymphocytes purified by immunomagnetic bead separation. They were not detected in buccal mucosa cells obtained by mouthwashes and in cultured skin fibroblasts examined in one of the patients. In both patients, this pattern of involvement suggests that the mtDNA mutation occurred in a self-renewing bone marrow stem cell with myeloid determination. Identification of two point mutations with very similar location suggests that cytochrome c oxidase plays an important role in the pathogenesis of AISA. COX may be the physiologic site of iron reduction and transport through the inner mitochondrial membrane.

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