Oxygen mitochondrial cytochromes

The purpose of sodium nitrite (or amyl nitrite in the absence of IV access) is to produce methemoglobin, which binds cyanide with greater affinity than mitochondrial cytochromes. In the presence of decreased oxygen carrying capacity, as in combined exposures to cyanide and carbon monoxide (e.g., some fires), sodium nitrite can be detrimental and should be avoided. 

Hydrogen sulfide inhibits mitochondrial cytochrome oxidase, resulting in disruption of the electron transport chain and impairing oxidative metabolism. Nervous and cardiac tissues, which have the highest oxygen demand (e.g., brain and heart), are especially sensitive to disruption of oxidative metabolism (Ammann 1986 Hall 1996). 

A). Cyanide ions (CN ) enter the organism in the form of hydrocyanic acid (HCN) the latter can be inhaled, released from cyanide salts in the acidic stomach juice, or enzymatically liberated from bitter almonds in the gastrointestinal tract The lethal dose of HCN can be as low as 50 mg. CN binds with high affinity to trivalent iron and thereby arrests utilization of oxygen via mitochondrial cytochrome oxidases of the respiratory chain An internal asphyxiation (histotoxic hypoxia) ensues while erythrocytes remain charged with O2 (venous blood colored bright red). 

The knowledge of these unique short iron-oxygen distances in ferryl compounds aids in identifying whether a compound has a ferryl structure. Thus the 580 nm compound formed upon addition of peroxide to mitochondrial cytochrome c oxidase has an iron-to-oxygen distance of 1.7 A, suggesting that it is a ferryl intermediate [117]. Of the two haem iron atoms in this molecule, one is unreactive to peroxide. Therefore it is possible to analyse an EXAFS spectrum of the peroxide-treated enzyme minus the spectrum of the untreated enzyme to determine this distance. However, clearly such difference EXAFS spectra will have increased errors associated with the estimate of iron-oxygen distances. 

Superoxide and HOOH are forms of toxic oxygen. Most superoxide and HOOH arising in the cell are undesirable byproducts of the mitochondrial cytochromes. Recently, toxic oxygen has been found to be used for cell signaling Irani 1997 ... 

Adiponitrile s mechanism of toxicity is similar to cyanide because it can potentially liberate cyanide in the body spontaneously. It forms a stable complex with ferric iron in the cytochrome oxidase enzymes, thereby inhibiting cellular respiration. Cyanide affects primarily the central nervous system (CNS), producing early stimulation followed by depression. It initially stimulates the peripheral chemoreceptors (causing increased respiration) and the carotid bodies (thereby slowing the heart). Early CNS, respiratory, and myocardial depression result in decreased oxygenation of the blood and decreased cardiac output. These effects produce both stagnation and hypoxemic hypoxia in addition to cytotoxic hypoxia from inhibition of mitochondrial cytochrome oxidase. 

C. E. Cooper, J. Torres, M. Sharpe, and M. T. Wilson, The Relationship of Oxygen Delivery to Absolute Hemoglobin Oxygenation and Mitochondrial Cytochrome Oxidase Redox State in the Adult Brain a Near-Infrared Spectroscopy Study, Biochem. J., 332, 627 (1998). 

L. Avila, H. Huang, C. O. Damaso, S. Lu, P. Moenne-Loccoz, M. Rivera, Coupled oxidation vs heme oxygenation Insights from axial ligand mutants of mitochondrial cytochrome b5, J. Am. Chem. Soc. 125 (2003) 4103. 

Biochemical mechanism Cyanide inhibits mitochondrial cytochrome oxidase, blocking electron transport and preventing oxygen utilization. Lactic acidosis results secondary to anaerobic metabolism. 

Cytochrome c-550(s) was partially purified by Ketchum et al. (1969). Afterward it was purified to an electrophoretically homogeneous state (Yamanaka et al., 1982), and its complete amino acid sequence was determined (Tanaka et al., 1982). Its molecular mass is 12.4 kDa. The cytochrome is very similar to mitochondrial cytochrome c (similarity, 40% 19%) on the basis of the sequence, and reacts with yeast cytochrome c peroxidase at the rate of 79% as fast as mitochondrial cytochrome c. Ferrocytochrome c-550(s) is oxidized very fast with molecular oxygen by the catalysis of N. winogradskyi cytochrome c oxidase turnover number is 117 s 1 (Yamanaka et al., 1982 Nomoto et al., 1993). 

When KZK< 10 2, which is a very common situation (e.g., when Hb02 serves as oxygen donor for mitochondrial cytochrome oxidase), KZK and 4KZ can be neglected and Equation (9) becomes ... 

Cytochrome oxidases are transmembrane protein complexes, which are localized at the inner mitochondrial membrane in eukaryotes or at the plasma membrane in bacteria. In addition to the reduction of oxygen, all cytochrome oxidases studied so far function as proton pumps as well, maintaining the proton gradient for the production of ATP [283 - 286]. While all cytochrome oxidases oxidize oxygen, they vary in their electron donors. Those receiving electrons from cytochrome c are called cytochrome c oxidases and those from ubiquinone ubiquinone oxidases [287]. 

The remarkable fact is that, despite these adaptations to minimize oxygen levels, some of these nitrogen-fixing bacteria, such as Bradyrhizo-bium japonicum, are still aerobic. They possess a form of cytochrome oxidase known as FixN, which has an extremely high affinity for oxygen. This enzyme is distantly related to mitochondrial cytochrome oxidase and probably evolved from a common ancestor. There is some evidence that the FixN oxidase is coupled functionally with leghaemoglobin,... 

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