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Oxidative phosphorylation or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine triphosphate (ATP). In eukaryotes, this takes place inside mitochondria. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is so pervasive because it releases more energy than alternative fermentation processes such as anaerobic glycolysis.
The cytochrome complex, or cyt c, is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion where it plays a critical role in cellular respiration. It transfers electrons between Complexes III and IV. Cytochrome c is highly water-soluble, unlike other cytochromes. It is capable of undergoing oxidation and reduction as its iron atom converts between the ferrous and ferric forms, but does not bind oxygen. It also plays a major role in cell apoptosis. In humans, cytochrome c is encoded by the CYCS gene.
Heme, or haem, is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver.
Cytochrome c peroxidase, or CCP, is a water-soluble heme-containing enzyme of the peroxidase family that takes reducing equivalents from cytochrome c and reduces hydrogen peroxide to water:
Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. It is the primary intracellular iron-storage protein in both prokaryotes and eukaryotes, keeping iron in a soluble and non-toxic form. In humans, it acts as a buffer against iron deficiency and iron overload.
Ceruloplasmin is a ferroxidase enzyme that in humans is encoded by the CP gene.
Rieske proteins are iron–sulfur protein (ISP) components of cytochrome bc1 complexes and cytochrome b6f complexes and are responsible for electron transfer in some biological systems. John S. Rieske and co-workers first discovered the protein and in 1964 isolated an acetylated form of the bovine mitochondrial protein. In 1979 Trumpower's lab isolated the "oxidation factor" from bovine mitochondria and showed it was a reconstitutively-active form of the Rieske iron-sulfur protein
It is a unique [2Fe-2S] cluster in that one of the two Fe atoms is coordinated by two histidine residues rather than two cysteine residues. They have since been found in plants, animals, and bacteria with widely ranging electron reduction potentials from -150 to +400 mV.
Enteropeptidase is an enzyme produced by cells of the duodenum and is involved in digestion in humans and other animals. Enteropeptidase converts trypsinogen into its active form trypsin, resulting in the subsequent activation of pancreatic digestive enzymes. Absence of enteropeptidase results in intestinal digestion impairment.
The prothrombinase complex consists of the serine protease, Factor Xa, and the protein cofactor, Factor Va. The complex assembles on negatively charged phospholipid membranes in the presence of calcium ions. The prothrombinase complex catalyzes the conversion of prothrombin (Factor II), an inactive zymogen, to thrombin (Factor IIa), an active serine protease. The activation of thrombin is a critical reaction in the coagulation cascade, which functions to regulate hemostasis in the body. To produce thrombin, the prothrombinase complex cleaves two peptide bonds in prothrombin, one after Arg271 and the other after Arg320. Although it has been shown that Factor Xa can activate prothrombin when unassociated with the prothrombinase complex, the rate of thrombin formation is severely decreased under such circumstances. The prothrombinase complex can catalyze the activation of prothrombin at a rate 3 x 105-fold faster than can Factor Xa alone. Thus, the prothrombinase complex is required for the efficient production of activated thrombin and also for adequate hemostasis.
Hephaestin, also known as HEPH, is a protein which in humans is encoded by the HEPH gene.
The iron-responsive element-binding proteins, also known as IRE-BP, IRBP, IRP and IFR , bind to iron-responsive elements (IREs) in the regulation of human iron metabolism.
Iron is an important biological element. It is used in both the ubiquitous Iron-sulfur proteins and in Vertebrates it is used in Hemoglobin which is essential for Blood and oxygen transport.
In enzymology, sarcosine dehydrogenase (EC 1.5.8.3) is a mitochondrial enzyme that catalyzes the chemical reaction N-demethylation of sarcosine to give glycine. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH group of donor with other acceptors. The systematic name of this enzyme class is sarcosine:acceptor oxidoreductase (demethylating). Other names in common use include sarcosine N-demethylase, monomethylglycine dehydrogenase, and sarcosine:(acceptor) oxidoreductase (demethylating). Sarcosine dehydrogenase is closely related to dimethylglycine dehydrogenase, which catalyzes the demethylation reaction of dimethylglycine to sarcosine. Both sarcosine dehydrogenase and dimethylglycine dehydrogenase use FAD as a cofactor. Sarcosine dehydrogenase is linked by electron-transferring flavoprotein (ETF) to the respiratory redox chain. The general chemical reaction catalyzed by sarcosine dehydrogenase is:
In enzymology, histidinol dehydrogenase (HIS4) (HDH) (EC 1.1.1.23) is an enzyme that catalyzes the chemical reaction
Calcium/calmodulin-dependent protein kinase type II gamma chain is an enzyme that in humans is encoded by the CAMK2G gene.
In enzymology, a myosin-heavy-chain kinase is an enzyme that catalyzes the chemical reaction
Ferritin light chain is a protein that in humans is encoded by the FTL gene. Ferritin is the major protein responsible for storing intracellular iron in prokaryotes and eukaryotes. It is a heteropolymer consisting of 24 subunits, heavy and light ferritin chains. This gene has multiple pseudogenes.
Adrenal ferredoxin is a protein that in humans is encoded by the FDX1 gene. In addition to the expressed gene at this chromosomal locus (11q22), there are pseudogenes located on chromosomes 20 and 21.
Mitochondrial ferritin is a ferroxidase enzyme that in humans is encoded by the FTMT gene.
Alpha-ketoglutarate-dependent hydroxylases are a major class of non-heme iron proteins that catalyse a wide range of reactions. These reactions include hydroxylation reactions, demethylations, ring expansions, ring closures, and desaturations. Functionally, the αKG-dependent hydroxylases are comparable to cytochrome P450 enzymes. Both use O2 and reducing equivalents as cosubstrates and both generate water.
References
- Cox JC, Boxer DH (1986). "The role of rusticyanin, a blue copper protein, in the electron transport chain of Thiobacillus ferrooxidans grown on iron or thiosulfate". Biotechnol. Appl. Biochem. 8: 269–275.
- Osaki S (November 1966). "Kinetic studies of ferrous ion oxidation with crystalline human ferroxidase (ceruloplasmin)". J. Biol. Chem. 241 (21): 5053–9. doi: 10.1016/S0021-9258(18)99669-9 . PMID 5925868.
- Osaki S, Walaas O (June 1967). "Kinetic studies of ferrous ion oxidation with crystalline human ferroxidase. II. Rate constants at various steps and formation of a possible enzyme-substrate complex". J. Biol. Chem. 242 (11): 2653–7. doi: 10.1016/S0021-9258(18)99620-1 . PMID 6027241.
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