Electron reactive oxygen species

One of the important consequences of neuronal stimulation is increased neuronal aerobic metabolism which produces reactive oxygen species (ROS). ROS can oxidize several biomoiecules (carbohydrates, DNA, lipids, and proteins). Thus, even oxygen, which is essential for aerobic life, may be potentially toxic to cells. Addition of one electron to molecular oxygen (O,) generates a free radical [O2)) the superoxide anion. This is converted through activation of an enzyme, superoxide dismurase, to hydrogen peroxide (H-iO,), which is, in turn, the source of the hydroxyl radical (OH). Usually catalase... 

Dimeric flavoprotein chromate reductases have been purified from Pseudomonas putida (ChrR) and Escherichia coli (YieF). The former produces a semiquinone and transiently reactive oxygen species, whereas the latter is an obligate four-electron reductant. One-electron reduction of Cr(Vl) to Cr(V) has, however, been observed as an intermediate in the reduction by the NAD(P)H-dependent reductase of Pseudomonas ambigua strain G-1 (Suzuki et al. 1992). 

Although reduction of chromate Cr to Cr has been observed in a number of bacteria, these are not necessarily associated with chromate resistance. For example, reduction of chromate has been observed with cytochrome Cj in Desulfovibrio vulgaris (Lovley and Phillips 1994), soluble chromate reductase has been purified from Pseudomonas putida (Park et al. 2000), and a membrane-bound reductase has been purified from Enterobacter cloacae (Wang et al. 1990). The flavoprotein reductases from Pseudomonas putida (ChrR) and Escherichia coli (YieF) have been purified and can reduce Cr(VI) to Cr(III) (Ackerley et al. 2004). Whereas ChrR generated a semi-quinone and reactive oxygen species, YieR yielded no semiquinone, and is apparently an obligate four-electron reductant. It could therefore present a suitable enzyme for bioremediation. 

Acutely, cells respond to low oxygen concentrations with changes in the function of ion channels and enzymes, and, in the case of enzymes involved in electron transport, the generation of reactive oxygen species. 

Mitochondria, nitric oxide synthase and arachidonic acid metabolism are sources of reactive oxygen species during ischemia-reperfusion injury. ROS generation during ischemia-reperfusion may come from several sources, including NOS activity, mitochondrial electron transport, multiple steps in the metabolism of arachidonic... 

XOR is a cytoplasmic enzyme and a ready source of electrons for transfer to molecular oxygen to form reactive oxygen species such as superoxide and peroxide. It is therefore thought to be involved in free radical-generated tissue injury and has been implicated in the pathogenesis of ischemia-reperfusion damage. Moreover, it has recently been implicated in the production of peroxynitrite (89), and carbonate radical anion (92), both potent biological oxidants. Its exact role in lipid peroxidation, inflammation, and infection needs... 

Mitochondrial function. NO is able to react with transition metals such as iron, including those contained within haem groups. Even at low NO concentrations there is competition between oxygen and NO for reversible binding to cytochrome c oxidase. If mitochondrial 02 is low respiration slows, which may confer anti-apoptotic benefit to the cell. As NO concentration rises and peroxynitrite is formed, electron transport is irreversibly inhibited, there is increased production of superoxide and other reactive oxygen species and apoptosis occurs. 

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