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Metabolomics

Electron Transport

Electron Transport

View IUBMB-Nicholson Animation of Membrane Respiratory Chain

A major source of cellular energy production, in the form of ATP, is derived from the proton motive force supplied to mitochondrial ATP synthase. The main driver of the proton gradient across the inner mitochondrial membrane is the electron transport system. NADH and FADH2 produced by glycolysis, fatty acid oxidation and the TCA cycle serve as a electron donors and cofactors for the protein complexes involved in the electron transport system. The net result is an influx of protons into the intermembrane space of the mitochondria and the production of water as a byproduct in the inner mitochondrial membrane.

2 H+ + 2 e+ + 1/2 O2 → H2O + energy

There are four membrane-bound protein complexes that participate in the electron transport system.

Complex I is a NADH dehydrogenase (or NADH-Coenzyme Q Reductase) composed of FMN, Coenzyme Q and Fe-S clusters. Using NADH as the initial electron donor, complex I generates a net result of 4 protons transferred from the matrix to the intermembrane space of the mitochondria, and the transfer of two electrons and two protons to reduce coenzyme Q located outside the complex within the inner mitochondrial membrane.

Complex II is Succinate Dehydrogenase (or Succinate-Coenzyme Q Reductase), which is one of the enzymes of the TCA cycle. It is composed of a bound FAD and three Fe-S clusters. Complex II generates a net result of the production of fumarate from succinate and reduction of one coenzyme Q located outside the complex within the inner mitochondrial membrane.

Complex III is a Cytochrome C Reductase (or Coenzyme Q -Cytochrome C Reductase). It is composed of cytochrome c1, cytochrome bL, cytochrome bH and a Fe-S Rieske protein. Complex III also contains two coenzyme Q binding sites, which utilize reduced coenzyme Q in two ways. The first step is to transfer electrons via the Fe-S protein to Cytochrome c1, which reduces cytochrome c. Secondly, the reduced coenzyme Q circulates electrons thru cytochrome c1, cytochrome bL and intermediate oxidative states of coenzyme Q resulting in the regeneration of one reduced coenzyme Q, one more reduced cytochrome c, and the translocation of four protons.

Complex IV is a Cytochrome c Oxidase. It is composed of heme-containing cytochrome a and cytochrome a3 plus two copper complexes. This complex generates a net result of the formation of two water molecules, the oxidation of four Cytochrome cs, and the translocation of two protons.

ATP Synthase is often termed Complex V of the electron transport system since it uses the proton motive force of the translocated protons to drive the nanomotor, which condenses ADP and phosphate to form ATP in the matrix.

Cytochrome c: Sigma's Cytochrome c products are supplied mainly in the oxidized form of the protein. The reduced form of cytochrome c can be prepared with either sodium dithionite or sodium ascorbate, followed by gel filtration. (See Dixon, H.B., and McIntosh, R., Nature, 213(74), 399-400 (1967))

Sigma employs two methods for purification of cytochrome c; either trichloroacetic acid (TCA) is used during preparation or acetic acid. The "TCA" procedure may reduce the amount of superoxide dismutase (SOD), but tends to cause dimerization or "acid-modified structures." In contrast the "acetic acid" method may have slightly higher amounts of SOD, but a lower percentage dimeric cytochrome c. Ion-exchange chromatography is used during purification. Any SOD present can readily be removed using size exclusion chromatography.

Related Sigma Products


Cytochromes
Enzymes and Kits
Antibodies
Cofactors and Substrates

Cytochromes
Product # Product Name Add to Cart
C1427 Cytochrome b5 human >90% (SDS-PAGE), recombinant, expressed in Escherichia coli (histidine-tagged)
C2037 Cytochrome c from bovine heart ≥95% as based on Mol. Wt. 12,327
C3131 Cytochrome c from bovine heart ≥95% as based on Mol. Wt. 12,327
C3006 Cytochrome c from bovine heart practical grade, ≥60% as based on Mol. Wt. 12,327
C4013 Cytochrome c from canine heart ≥95% as based on Mol. Wt. 12,241
C0761 Cytochrome c from chicken heart ≥95% as based on Mol. Wt. 12,222
C7752 Cytochrome c from equine heart ≥95% as based on Mol. Wt. 12,384
C2506 Cytochrome c from equine heart ≥95% (SDS-PAGE)
C2867 Cytochrome c from equine heart ≥99% (SDS-PAGE)
C3256 Cytochrome c from equine heart ~90% as based on EmM550 = 27.8 and Mol. Wt. = 12,384
C3483 Cytochrome c human >95% (SDS-PAGE), lyophilized powder
C4011 Cytochrome c from pigeon breast muscle ≥95% as based on Mol. Wt. 12,173
C9136 Cytochrome c from rabbit heart ≥95% as based on Mol. Wt. 12,220
C7892 Cytochrome c from rat heart ≥95% as based on Mol. Wt. 12,132
C2436 Cytochrome c from Saccharomyces cerevisiae ≥85% as based on Mol. Wt. 12,588
C4186 Cytochrome c partially acetylated from equine heart lyophilized powder
Enzymes and Kits back to top
Product # Product Name Add to Cart
CYTOCOX1 Cytochrome c Oxidase Assay Kit
C3381 Cytochrome c reductase from porcine heart Type I, lyophilized powder, ≥1.0 units/mg protein
CY0100 Cytochrome c Reductase [NADPH] Assay Kit 1 kit sufficient for 100 tests
Antibodies back to top
Product # Product Name Add to Cart
C5723 Anti-Cytochrome c antibody produced in sheep whole antiserum
Cofactors and Substrates back to top
Product # Product Name Add to Cart
A2754 Adenosine 5′-diphosphate sodium salt bacterial, 95-99%
A2383 Adenosine 5′-triphosphate disodium salt Grade I, ≥99%, from microbial source
F6625 Flavin adenine dinucleotide disodium salt hydrate ≥95% (HPLC), powder
F8399 Riboflavin 5′-monophosphate sodium salt dihydrate ~95% (HPLC)
N1636 β-Nicotinamide adenine dinucleotide hydrate ≥99%
N8129 β-Nicotinamide adenine dinucleotide, reduced disodium salt hydrate ~98%
S2378 Sodium succinate dibasic hexahydrate ReagentPlus, ≥99%
F1506 Sodium fumarate dibasic
F1506 9-Fluorenone 98%
C7956 Coenzyme Q1 ≥95%
C8081 Coenzyme Q2 ≥90%
C2470 Coenzyme Q4 ≥90%
C9504 Coenzyme Q6 from Saccharomyces cerevisiae
C9888 Coenzyme Q9 from Candida utilis 90-95%
C9538 Coenzyme Q10 ≥98% (HPLC)
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