cytochrome

Information about cytochrome

Cytochromes are generally membrane-bound hemoproteins that contain heme groups and carry out electron transport.

They are either found as monomeric proteins (i.e. cytochrome c) or as subunits of bigger enzymatic complexes that catalyze redox reactions. They are found in the mitochondrial inner membrane and endoplasmic reticulum of eukaryotes, in the chloroplasts of plants, in photosynthetic microorganisms, and in bacteria.

Structure and function

The heme group is a highly conjugated ring system (which means its electrons are very mobile) surrounding a metal ion, which readily interconverts between the oxidation states. For many cytochromes the metal ion present is that of iron, which interconverts between Fe²⁺ (reduced) and Fe³⁺ (oxidized) states (electron-transfer processes) or between Fe²⁺ (reduced) and Fe³⁺ (formal, oxidized) states (oxidative processes). Cytochromes are thus capable of performing oxidation and reduction. Because the cytochromes (as well as other complexes) are held within membranes in an organized way, the redox reactions are carried out in the proper sequence for maximum efficiency.

In the process of oxidative phosphorylation, which is the principal energy-generating process undertaken by organisms which need oxygen to survive, other membrane-bound and soluble complexes and cofactors are involved in the chain of redox reactions, with the additional net effect that protons (H⁺) are transported across the mitochondrial inner membrane. The resulting transmembrane proton gradient [(protonmotive force)] is used to generate ATP, which is the universal chemical energy currency of life. ATP is consumed to drive cellular processes that require energy (such as synthesis of macromolecules, active transport of molecules across the membrane, and assembly of flagella).

Types

Several kinds of cytochrome exist and can be distinguished by spectroscopy, exact structure of the heme group, inhibitor sensitivity, and reduction potential.

Three types of cytochrome are distinguished by their prosthetic groups:

Type	prosthetic group
Cytochrome a	heme a
Cytochrome b	heme b
Cytochrome d	tetrapyrrolic chelate of iron^[1]

The definition of cytochrome c is not defined in terms of the heme group.^[2] There is no "cytochrome e", but there is a cytochrome f, which is often considered a type of cytochrome c.^[3]

In mitochondria and chloroplasts, these cytochromes are often combined in electron transport and related metabolic pathways:

Cytochromes	Combination
a and a₃	Cytochrome c oxidase ("Complex IV")
b and c₁	Coenzyme Q - cytochrome c reductase ("Complex III")
b₆ and f	Plastoquinol—plastocyanin reductase

A completely distinct family of cytochromes are known as the cytochrome P450 oxidases, so named for the characteristic Soret peak formed by absorbance of light at wavelengths near 450 nm when the heme iron is reduced (with sodium dithionite) and complexed to carbon monoxide. These enzymes are primarily involved in steroidogenesis and detoxification.

References

1. ^ MeSH Cytochrome+d
2. ^ MeSH Cytochrome+c+Group.
3. ^ Cytochrome at eMedicine Dictionary

External links

A hemoprotein (also haemoprotein), or heme protein, is a metalloprotein containing a heme prosthetic group, either covalently or noncovalently bound to the protein itself.
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A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as
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electron transport chain associates electron carriers (such as NAD⁺ and FADH2) and mediating biochemical reactions that produce adenosine triphosphate (ATP), which is the energy currency of life.
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In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or "coassembles") with other protein molecules to form a multimeric or oligomeric protein.
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Cytochrome c, or cyt c (horse heart: PDB 1HRC ) is a small heme protein found loosely associated with the inner membrane of the mitochondrion. It is a soluble protein, unlike other cytochromes, and is an essential component of the electron transfer chain.
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Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed.

This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide, or the
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Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide to produce sugars, the raw material for energy and biomass production in all green plants
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microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of microorganisms is called microbiology.
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Bacteria

Phyla

Actinobacteria
Aquificae
Chlamydiae
Bacteroidetes/Chlorobi
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Deinococcus-Thermus
Dictyoglomi
Fibrobacteres/Acidobacteria
Firmicutes
Fusobacteria
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Electron

Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Composition: Elementary particle
Family: Fermion
Group: Lepton
Generation: First
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3, 4, 6
(amphoteric oxide)
Electronegativity 1.83 (Pauling scale)
Ionization energies
(more) 1st: 762.5 kJmol⁻¹
2nd: 1561.9 kJmol⁻¹
3rd: 2957 kJmol⁻¹

Atomic radius 140 pm
Atomic radius (calc.
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Electron transfer (ET) is the process by which an electron moves from one atom or molecule to another atom or molecule. ET is a mechanistic description of the thermodynamic concept of redox, wherein the formal oxidation states of both reaction partners change.
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Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate (ATP). Although the many forms of life on Earth utilize a range of different nutrients, almost all carry out oxidative phosphorylation to
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complex in chemistry usually is used to describe molecules or ensembles formed by the combination of ligands and metal ions. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds.
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Cofactor may refer to any of the following:

Cofactor (linear algebra) The signed minor of a matrix
Minor (linear algebra) as an alternative name for the determinant of a smaller matrix than that which it describes

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In cellular biology, an electrochemical gradient refers to the electrical and chemical properties across a membrane. These are often due to ion gradients, particularly proton gradients, and can represent a type of potential energy available for work in a cell.
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Adenosine 5'-triphosphate (ATP) is a multifunctional nucleotide that is most important as a "molecular currency" of intracellular energy transfer. In this role, ATP transports chemical energy within cells for metabolism.
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For the insect anatomical structure, see .

A flagellum (plural: flagella) is a long, slender projection from the cell body, composed of microtubules and surrounded by the plasma membrane.
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Heme A differs from heme B in that a methyl side chain at ring position 8 is oxidized into a formyl group, and one of the vinyl side chains, at ring position 2, has been replaced by an isoprenoid chain.
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Heme B is the most abundant heme; both hemoglobin and myoglobin are examples of oxygen transport proteins that contain heme B and the peroxidase family of enzymes also contain heme B.
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Chelation (from Greek χηλή, chelÃ¨, meaning claw; pronounced [ˌki:ˈleɪʃən]) is the binding or complexation of a bi- or multidentate ligand.
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