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the 1st letter of the Roman alphabet (同)a
the blood group whose red cells carry the A antigen (同)type_A, group A
a public promotion of some product or service (同)advertisement, advertizement, advertising, advertizing, advert
(biochemistry) a class of hemoprotein whose principal biological function is electron transfer (especially in cellular respiration)

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answer / ampere
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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/05/15 16:01:57」(JST)

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Cytochrome c with heme c.

Cytochromes are, in general, membrane-bound (i.e. inner mitochondrial membrane) hemeproteins containing heme groups and are primarily responsible for the generation of ATP via electron transport.

They are found either as monomeric proteins (e.g., cytochrome c) or as subunits of bigger enzymatic complexes that catalyze redox reactions.

History [edit]

Cytochromes were initially described in 1884 by MacMunn as respiratory pigments (myohematin or histohematin).^[1] In the 1920s, Keilin rediscovered these respiratory pigments and named them the cytochromes, or “cellular pigments”, and classified these heme proteins, on the basis of the position of their lowest energy absorption band in the reduced state, as cytochromes a (605 nm), b (~565 nm), and c (550 nm). The UV-visible spectroscopic signatures of hemes are still used to identify heme type from the reduced bis-pyridine-ligated state, i.e., the pyridine hemochrome method. Within each class, cytochrome a, b, or c, early cytochromes are numbered consecutively, e.g. cyt c, cyt c₁, and cyt c₂, with more recent examples designated by their reduced state R-band maximum, e.g. cyt c₅₅₉.^[2]

Structure and function [edit]

The heme group is a highly-conjugated ring system (which allows its electrons to be 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⁺ (oxidised) 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, 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 [edit]

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^[3]

The definition of cytochrome c is not defined in terms of the heme group.^[4] There is no "cytochrome e," but there is a cytochrome f, which is often considered a type of cytochrome c.^[5]

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") with electrons delivered to complex by soluble cytochrome c (hence the name)
b and c₁	Coenzyme Q - cytochrome c reductase ("Complex III")
b₆ and f	Plastoquinol—plastocyanin reductase

A completely distinct family of cytochromes is 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 [edit]

^ Mac Munn, C. A (1886). "Researches on Myohaematin and the Histohaematins". Philosophical Transactions of the Royal Society of London (The Royal Society) 177 (0): 267–298. doi:10.1098/rstl.1886.0007. JSTOR 109482.
^ Reedy, C. J. & Gibney, B. R. (February 2004). "Heme protein assemblies". Chem Rev 104 (2): 617–49. doi:10.1021/cr0206115. PMID 14871137.
^ Cytochrome d at the US National Library of Medicine Medical Subject Headings (MeSH)
^ Cytochrome c Group at the US National Library of Medicine Medical Subject Headings (MeSH).
^ Cytochrome at eMedicine Dictionary

External links [edit]

Scripps Database of Metalloproteins
Cytochromes at the US National Library of Medicine Medical Subject Headings (MeSH)

UpToDate Contents

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English Journal

Mitochondrial activity, hemocyte parameters and lipid composition modulation by dietary conditioning in the Pacific oyster Crassostrea gigas.

Dudognon T1, Lambert C, Quere C, Auffret M, Soudant P, Kraffe E.Author information 1Laboratoire des Sciences de l'Environnement Marin, Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, UMR 6539 CNRS/UBO/IRD/IFREMER, 29280, Plouzané, France.AbstractSeveral parameters can affect membrane lipid composition in bivalves, including diet. Although two fatty acids (FA) 22:6n-3 and 20:5n-3 are essential membrane components, they are sparingly synthesized by bivalves and must be obtained from their diet. Here, effects of dietary modifications of membrane lipid composition were studied at both cellular and subcellular levels in the oyster Crassostrea gigas. To this end, we compared oysters fed two monoalgal diets that differed markedly in their FA composition and a mix of both. As expected, algae impacted phospholipids, in particular 22:6n-3 and 20:5n-3, reflecting differences of dietary microalgae FA composition. Meantime, total saturated FA, total monounsaturated FA, total polyunsaturated FA and total non-methylene-interrupted FA varied little and phospholipid class composition was only slightly affected by diets. Measures made in hemocytes indicated that only mitochondrial membrane potential was affected by diets. Total ROS production as well as mitochondrial superoxide production did not differ with diet. There was no difference in phosphorylating (state 3) and non-phosphorylating (state 4) rates of oxygen consumption rates or in cytochrome c oxidase activity of mitochondria isolated from gills between the three diets. Similarly, neither cytochromes a, b, c or c 1 content nor citrate synthase activities were changed, suggesting that number and morphology of mitochondria were not affected by dietary treatment. These results suggest that oysters could possess high homeostatic capabilities, at both cellular and subcellular levels, to minimize the effect of dietary FA and related membrane lipid FA modifications on mitochondrial functions. These capabilities could be a means to face variations in diet composition in their natural environment and to preserve important oyster physiological functions such as growth and reproduction.
Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology.J Comp Physiol B.2014 Apr;184(3):303-17. doi: 10.1007/s00360-013-0800-1. Epub 2014 Jan 18.
Several parameters can affect membrane lipid composition in bivalves, including diet. Although two fatty acids (FA) 22:6n-3 and 20:5n-3 are essential membrane components, they are sparingly synthesized by bivalves and must be obtained from their diet. Here, effects of dietary modifications of membra
PMID 24441864

A possible role of Aspergillus niger mitochondrial cytochrome c in malachite green reduction under calcium chloride stress.

Gomaa OM1, Selim NS, Linz JE.Author information 1Microbiology Department, National Center for Radiation Research and Technology (NCRRT), Atomic Energy Authority, 3 Ahmad El Zomor St., Nasr City, Cairo, 11371, Egypt, ola_gomaa@hotmail.com.AbstractIn previous work, decolorization of malachite green (MG) was studied in Aspergillus niger in the presence and absence of calcium chloride stress. Decolorization took place within 24 h, and a signal transduction process that initiated MG decolorization was suggested to be involved. In the present study, further investigation of the relationship between calcium chloride stress and enhanced MG biodegradation was conducted at the sub-cellular level. MG-NADH reductase activity, a key enzyme in MG decolorization, was produced as decolorization commenced, and enzyme activity increased threefold upon exposure to calcium chloride. Inhibitors of cytochrome p450, Ca(2+) channel activity as well as activity of the signaling protein phosphoinositide 3-kinase were tested. All three activities were inhibited to different extents resulting in reduced MG decolorization. Spectral analysis of the mitochondrial fraction showed a heme signal at 405 nm and A405/A280 ratio that is characteristic of the porphoryin ring of cytochromes. There were no peaks detected for cytochromes a or b, but a shoulder appearing at 550 nm was observed, which suggested that cytochrome c is involved; the absorbance for cytochrome c doubled after calcium chloride stress supporting this idea. MG decolorization took place via a series of demethylation steps, and cytotoxicity analysis revealed a decrease in the toxicity associated with generation of leucomalachite green.
Cell biochemistry and biophysics.Cell Biochem Biophys.2013 Dec;67(3):1291-9. doi: 10.1007/s12013-013-9661-1.
In previous work, decolorization of malachite green (MG) was studied in Aspergillus niger in the presence and absence of calcium chloride stress. Decolorization took place within 24 h, and a signal transduction process that initiated MG decolorization was suggested to be involved. In the present stu
PMID 23737340

Impact of genetic polymorphism on drug-drug interactions mediated by cytochromes: a general approach.

Tod M1, Nkoud-Mongo C, Gueyffier F.Author information 1Hospices Civils de Lyon, Université de Lyon, Université Lyon 1, 69000, Lyon, France, michel.tod@chu-lyon.fr.AbstractCurrently, quantitative prediction of the impact of genetic polymorphism and drug-drug interactions mediated by cytochromes, based on in vivo data, is made by two separate methods and restricted to a single cytochrome. We propose a unified approach for describing the combined impact of drug-drug interactions and genetic polymorphism on drug exposure. It relies on in vivo data and uses the following three characteristic parameters: one for the victim drug, one for the interacting drug, and another for the genotype. These parameters are known for a wide range of drugs and genotypes. The metrics of interest are the ratio of victim drug area under the curve (AUC) in patients with genetic variants taking both drugs, to the AUC in patients with either variant or wild-type genotype taking the victim drug alone. The approach was evaluated by external validation, comparing predicted and observed AUC ratios found in the literature. Data were found for 22 substrates, 30 interacting drugs, and 38 substrate-interacting drug couples. The mean prediction error of AUC ratios was 0.02, and the mean prediction absolute error was 0.38 and 1.34, respectively. The model may be used to predict the variations in exposure resulting from a number of drug-drug-genotype combinations. The proposed approach will help (1) to identify comedications and population at risk, (2) to adapt dosing regimens, and (3) to prioritize the clinical pharmacokinetic studies to be done.
The AAPS journal.AAPS J.2013 Oct;15(4):1242-52. doi: 10.1208/s12248-013-9530-2. Epub 2013 Sep 12.
Currently, quantitative prediction of the impact of genetic polymorphism and drug-drug interactions mediated by cytochromes, based on in vivo data, is made by two separate methods and restricted to a single cytochrome. We propose a unified approach for describing the combined impact of drug-drug int
PMID 24027036