Metabolism of oxygen

METABOLISM OF OXYGEN HETEROCYCLES 1.09.4.1 Metabolic Options open to Oxygen Heterocycles... 

Fig. 1. Two-compartment model to describe the metabolism of oxygen-derived free radicals in myocardial tissue. This figure depicts the progressive reduction of intracellular oxygen during the cycle of ischemia and reperfusion. Inhibitors of radical metabolism are shown in dashed boxes. Radical spin traps are shown in closed boxes.

Nakatani, T., Kosugi, Y., Mori, A., Tajimi, K., and Kobayashi, K., Changes in the metabolism of oxygen metabolism in a course recovering from potassium cyanide. Am. J. Emerg. Med., 11, 213-217, 1993. 

NakataniT, Kosugi Y, Mori A et al. (1993). Changes in the metabolism of oxygen metabolism in a clinical... 

Considerable effort has been devoted to the bacterial metabolism of oxygenated compounds including phenol, catechol, benzoate, and hydroxyben-zoates which are much more readily degraded than the parent hydrocarbons, and some of the details have been tacitly assumed in the foregoing discussion. An account of the appropriate oxygenases has been given in Chapter 4, Section 4.4.2, so that only a brief summary of the initial reactions is justified here. 

When, however, 13(S)-HPOD was incubated with an ammonium sulphate precipitate of defatted com germ, the resulting 12-oxo-PDA was not optically pure but a mixture of enantiomers in a ratio of 82.18 [35]. The 12-oxo-PDA obtained by incubation of 13(S)-HPOT with flaxseed extracts was found to be a racemic mixture [36]. These results may be due to low or absent allene oxide cyclase activity in the preparations used [34]. The allene oxide cyclase, a novel enzyme in the metabolism of oxygenated fatty acids was partially characterised and found to be a soluble protein with an apparent molecular weight of about 45 kDa which catalysed specifically the conversion of allene oxide into 12-oxo-PDA [34]. The allene oxide was very unstable and was rapidly hydrolysed in aqueous media into stable 12-oxo-13-hydroxy-9(z),15(z)-octadecadienoic acid (a-ketols) [34]. 

The researchers extended the Kety-Schmidt method to the use of chemically inert radioactive tracers, krypton-79 and xenon-133, because it was easier to measure their concentrations in blood. Later, oxygen-15 and xenon-133 were used to measure regional blood flow to the brain. Oxygen-15 made it possible to measure the rate of metabolism of oxygen to carbon dioxide. Oxygen-15 is produced in a cyclotron, its use complicated by its short (2.5 min) half-life. 

During metabolism of oxygen to water in the mitochondria, a small fraction of the oxygen is reductively converted into superoxide as a by-product. Superoxide may be further converted into various ROS, i.e., hydroxyl radical, hydrogen peroxide and others. 

Mitochondrial reduced glutathione (GSH) plays an important role in the maintenance of cell functions and viability by metabolism of oxygen free radicals generated by the respiratory chain. Mar et al. (2002) showed that the ability of pyruvate to protect against a loss of GSH in HepG2 cells treated with buthionine sulphoximine (BSO), a specific inhibitor of the rate-limiting enzyme in GSH synthe-... 

The oxidations carried out by plant tissues are more varied in character than those in animal systems (cf. James, 1957). In particular, the importance of cytochrome oxidase, which is responsible for nearly all the oxygen uptake of animal cells, seems much diminished in the case of plant respiration. One of the traditional problems facing the plant physiologist has therefore been the discovery of the other systems in plants involved in the metabolism of oxygen. 

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