Superoxide anion free radical

Transfer of a single electron to O2 generates the potentially damaging superoxide anion free radical (02 ), the destructive effects of which are amphfied by its giv-... 

Konaka R, Kasahara E, Dunlap WC, Yamamoto Y, Chen KC, Inoue M. Irradiation of titanium dioxide generates both singlet oxygen and superoxide anion. Free Radic Biol Med 1999 27 294—300. 

Dopamine- -hydroxylase is another copper enzyme that plays a major function in the biosynthesis of norepinephrine (40). A protective catalyst, superoxide dismutase, has been described to catalyze the dismu-tation of the superoxide anion free radical (41). Other enzymes known to contain copper are the laccases, the phenol oxidases, and the ascorbic acid oxidases (12). 

The lung also possesses nonenzymatic antioxidants such as vitamin E, beta-carotene, vitamin C, and uric acid. Vitamin E is lipid-soluble and partitions into lipid membranes, where it is positioned optimally for maximal antioxidant effectiveness. Vitamin E converts superoxide anion, hydroxyl radical, and lipid peroxyl radicals to less reactive oxygen metabolites. Beta-carotene also accumulates in cell membranes and is a metabolic precursor to vitamin A. Furthermore, it can scavenge superoxide anion and react directly with peroxyl-free radicals, thereby serving as an additional lipid-soluble antioxidant. Vitamin C is widely available in both extracellular and intracellular spaces where it can participate in redox reactions. Vitamin C can directly scavenge superoxide and hydroxyl radical. Uric acid formed by the catabolism of purines also has antioxidant properties and primarily scavenges hydroxyl radical and peroxyl radicals from lipid peroxidation. 

A free radical is an atom or molecule that possesses one or more unpaired electrons. Since electrons are more stable when paired together in orbitals, radicals are generally unstable and are therefore highly reactive with a variety of substrates. Free radicals of importance in biological systems include reactive oxygen species (ROS) and reactive nitrogen species (RNS). ROS include superoxide anion hydroxyl radical ("OH),... 

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... 

NADH, which enters the Krebs cycle. However, during cerebral ischaemia, metabolism becomes anaerobic, which results in a precipitous decrease in tissue pH to below 6.2 (Smith etal., 1986 Vonhanweh etal., 1986). Tissue acidosis can now promote iron-catalysed free-radical reactions via the decompartmentalization of protein-bound iron (Rehncrona etal., 1989). Superoxide anion radical also has the ability to increase the low molecular weight iron pool by releasing iron from ferritin reductively (Thomas etal., 1985). Low molecular weight iron species have been detected in the brain in response to cardiac arrest. The increase in iron coincided with an increase in malondialdehyde (MDA) and conjugated dienes during the recirculation period (Krause et al., 1985 Nayini et al., 1985). 

It has already been stressed that the discovery of superoxide as the enzymatically produced diffusion-free dioxygen radical anion [1-3] was a pivotal event in the study of free radical processes in biology. It is not of course that the McCord and Fridovich works were the first ones in free radical biology, but the previous works were more of hypothetical character, and only after the identification of superoxide by physicochemical, spectral, and biochemical analytical methods the enzymatic superoxide production became a proven fact. 

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