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Cytochrome c
 
 
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Cytochrome c, or cyt c (horse heart: PDB
Protein Data Bank

The Protein Data Bank is a repository for the 3-D structural data of large biological molecules, such as proteins and nucleic acids. . The data, typically obtained by X-ray crystallography or Protein NMR and submitted by biologists and biochemistry from around the world, are released into the public domain, and can be accessed at no charge...
 ) is a small heme
Heme

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....
 protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
 found loosely associated with the inner membrane of the mitochondrion
Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryote cell . These organelles range from 0.5–10 micrometers in diameter....
. It belongs to the cytochrome c family
Cytochrome c family

Cytochromes c are electron-transfer proteins having one or several heme c groups, bound to the protein by one or, more generally, two thioether bonds involving sulphydryl groups of cysteine residues....
 of proteins. Cytochrome c is a highly soluble protein, unlike other cytochrome
Cytochrome

Cytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as subunitss or as subunits of bigger enzymatic complexes that catalyze redox reactions....
s, with a solubility of about 100g/L and is an essential component of the electron transport chain
Electron transport chain

An electron transport chain couples a chemical reaction between an electron donor and an electron acceptor to the transfer of proton across a Cell membrane, through a set of mediating biochemical reactions....
, where it carries one electron.






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Cytochrome c, or cyt c (horse heart: PDB
Protein Data Bank

The Protein Data Bank is a repository for the 3-D structural data of large biological molecules, such as proteins and nucleic acids. . The data, typically obtained by X-ray crystallography or Protein NMR and submitted by biologists and biochemistry from around the world, are released into the public domain, and can be accessed at no charge...
 ) is a small heme
Heme

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....
 protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
 found loosely associated with the inner membrane of the mitochondrion
Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryote cell . These organelles range from 0.5–10 micrometers in diameter....
. It belongs to the cytochrome c family
Cytochrome c family

Cytochromes c are electron-transfer proteins having one or several heme c groups, bound to the protein by one or, more generally, two thioether bonds involving sulphydryl groups of cysteine residues....
 of proteins. Cytochrome c is a highly soluble protein, unlike other cytochrome
Cytochrome

Cytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as subunitss or as subunits of bigger enzymatic complexes that catalyze redox reactions....
s, with a solubility of about 100g/L and is an essential component of the electron transport chain
Electron transport chain

An electron transport chain couples a chemical reaction between an electron donor and an electron acceptor to the transfer of proton across a Cell membrane, through a set of mediating biochemical reactions....
, where it carries one electron. It is capable of undergoing oxidation and reduction
Redox

Redox describes all chemical reactions in which atoms have their oxidation number changed.This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane , or it can be a complex process such as the oxidation of sugar in the human body through a ser...
, but does not bind oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
. It transfers electrons between Complexes III
Coenzyme Q - cytochrome c reductase

The coenzyme Q : cytochrome c ? oxidoreductase, sometimes called the cytochrome bc1 complex, and at other times complex III, is the third complex in the electron transport chain , playing a critical role in biochemical generation of ATP ....
 and IV
Cytochrome c oxidase

The enzyme cytochrome c oxidase or Complex IV is a large transmembrane protein complex found in bacteria and the mitochondrion.It is the last enzyme in the respiratory electron transport chain of mitochondria located in the mitochondrial membrane....
.

Variation


Cytochrome c is a highly conserved protein across the spectrum of species, found in plants, animals, and many unicellular organisms. This, along with its small size (molecular weight about 12,000 daltons), makes it useful in studies of cladistics
Cladistics

Cladistics is the hierarchical classification of species based on evolutionary ancestry. Cladistics is distinguished from other taxonomic systems because it focuses on evolution rather than similarities between species, and because it places heavy emphasis on objective, quantitative analysis....
. Its primary structure consists of a chain of about 100 amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
s. Many higher order organisms possess a chain of 104 amino acids.

The cytochrome c molecule has been studied for the glimpse it gives into evolutionary biology. Both chicken
Chicken

The chicken is a Domestication fowl. Recent evidence suggests that domestication of the chicken was under way in Vietnam over 10,000 years ago....
s and turkey
Turkey

Turkey , known officially as the Republic of Turkey , is a Eurasian country that stretches across the Anatolian peninsula in southwest Asia and Thrace in the Balkans region of Southern Europe....
s have identical sequence homology (amino acid for amino acid), whereas duck
Duck

Duck is the common name for a number of species in the Anatidae family of birds. The ducks are divided between several subfamilies listed in full in the Anatidae article; they do not represent a clade but a form taxon, being the Anatidae not considered swans and goose....
s possess molecules differing by one amino acid. Similarly, both human
Human

A human being, also human or man, is a member of a species of bipedalism primates in the family Hominidae . Mitochondrial DNA evidence indicates that modern humans originated in east Africa about 200,000 years ago....
s and chimpanzee
Chimpanzee

Chimpanzee, sometimes colloquially known as a chimp, is the common name for the two Extant taxon species of ape in the genus Pan where the Congo River forms the boundary between the native habitat of the two species:...
s have the identical molecule, while rhesus monkeys share all but one of the amino acids: the 66th amino acid is isoleucine
Isoleucine

Isoleucine is an a-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be part of our diet....
 in the former and threonine
Threonine

Threonine is an a-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as Chemical polarity....
 in the latter. Pig
Pig

Pigs, also called hogs or swine, are a genus of even-toed ungulates within the Family Suidae. The name pig, hog, or swine most commonly refers to the Domestic pig in everyday parlance, but technically encompasses several distinct species, including the Wild Boar....
s, cows and sheep
Sheep

#REDIRECT Domestic sheep...
 also share identical cytochrome c molecules.

Functions

Cytochrome c can catalyze several reactions such as hydroxylation
Hydroxylation

Hydroxylation is any chemistry process that introduces one or more hydroxyl groups into a compound thereby oxidation it. In biochemistry, hydroxylation reactions are often facilitated by enzymes called hydroxylases....
 and aromatic oxidation, and shows peroxidase
Peroxidase

Peroxidases are a large family of enzymes. A majority of peroxidase protein sequences can be found in the PeroxiBase database. Peroxidases typically catalyze a reaction of the form:...
 activity by oxidation of various electron donors such as 2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS
ABTS

In biochemistry, 2,2'-azino-bis or ABTS is chemical compound used to observe the enzyme kinetics of specific enzymes. A common use for it is in the enzyme-linked immunosorbent assay to detect for binding of molecules to each other....
), 2-keto-4-thiomethyl butyric acid and 4-aminoantipyrine.

Role in low level laser therapy (LLLT) / Photobiomodulation

Cytochrome c is also suspected to be the functional complex in so called LLLT: Low-level laser therapy. In LLLT, red light and some near infra-red wavelengths penetrate tissue in order to increase cellular regeneration. Light of this wavelength appears capable of increasing activity of cytochrome c, thus increasing metabolic activity and freeing up more energy for the cells to repair the tissue.

Role in apoptosis

Cytochrome c is also an intermediate in apoptosis
Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
, a controlled form of cell death used to kill cells in the process of development or in response to infection or DNA damage.

Cytochrome c is released by the mitochondria in response to pro-apoptotic stimuli. The sustained elevation in calcium
Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
 levels precedes cyt c release from the mitochondria. The release of small amounts of cyt c leads to an interaction with the IP3 receptor
Inositol triphosphate receptor

Inositol triphosphate receptor is a membrane glycoprotein complex acting as calcium channel activated by inositol triphosphate . The IP3 receptor was first purified from rat cerebellum....
 (IP3R) on the endoplasmic reticulum
Endoplasmic reticulum

The endoplasmic reticulum is a eukaryote organelle that forms an interconnected network of tubules, vesicle , and cisternae within cell . The lacey membranes of the endoplasmic reticulum were first seen by Keith R....
 (ER), causing ER calcium release. The overall increase in calcium triggers a massive release of cyt c, which then acts in the positive feedback loop to maintain ER calcium release through the IP3Rs. This explains how the ER calcium release can reach cytotoxic levels. This release of cytochrome c in turn activates caspase 9, a cysteine protease
Protease

A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain, which form a molecule of protein....
. Caspase 9 can then go on to activate caspase 3
Caspase 3

Caspase 3 is a caspase protein which interacts with caspase 8....
 and caspase 7
Caspase 7

Caspase-7, apoptosis-related cysteine peptidase, also known as CASP7, is a human protein and gene....
, which are responsible for destroying the cell from within.

Classes

In 1991 R. P. Ambler recognized four classes of cytochrome c:

  • Class I includes the low­spin soluble cytochrome c of mitochondria and bacteria. It has the heme-­attachment site towards the N­ terminus of histidine and the sixth ligand provided by a methionine residue towards the C ­terminus.


  • Class II includes the high­spin cytochrome c'. It has the heme-attachment site closed to the N terminus of histidine.


  • Class III comprises the low redox potential multiple­ heme cytochromes. The heme c groups are structurally and functionally nonequivalent and present different redox potentials in the range 0 to -400 mV.


  • Class IV was originally created to hold the complex proteins that have other prosthetic groups as well as heme c.


Further reading



Additional images


See also

  • PEGylation
    PEGylation

    PEGylation is the process of covalent attachment of Polyethylene glycol polymer chains to another molecule, normally a drug or therapeutic protein....


External links

  • - PMAP The Proteolysis Map
    The Proteolysis Map

    The Proteolysis MAP is an integrated web resource focused on proteases....
    -animation
- Calculated orientations of cytochromes c in the lipid bilayer