Aerobic mechanism

Vinyl acetate is slightly or moderately toxic to humans and animals. The vapor irritates the eyes starting with 20 ppm, while the detection threshold is reported to be about 0.5 ppm. Released into the environment the vinyl acetate evaporates easily, being degraded rapidly by photochemical reactions, as well as biodegraded by either anaerobic or aerobic mechanisms. Therefore, the bioaccumulahon of vinyl acetate in the ecosphere is unlikely. 

Continued depletion of L-ascorbic acid in stored fruit-juices may be partly due to interaction with the hydrogen peroxide initially produced by aerobic mechanisms. Indeed, introduction of hydrogen peroxide, in amounts equivalent to the L-ascorbic acid content, into three-month old, blackcurrant-juice samples, caused a 50% loss of L-ascorbic acid in one hour, probably ascribable to formation of dehydro-L-ascorbic acid. 

Anzenbacher, R, T. Niwa, L.M. Tolbert, S.R. Sirimanne, and F.P. Guengerich (1996). Oxidation of 9-alkylanthracenes by cytochrome P450 2B1, horseradish peroxidase, and iron tetraphenylpor-phine/iodosylbenzene systems Anaerobic and aerobic mechanisms. Biochemistry 35, 2512-2520. 

Oxygenated derivatives of carotenoids also are common and widely distributed. These colored substances are known collectively as xanthophylls. The formation of xanthophylls involves an aerobic mechanism. p-Carotene is converted oxidatively to lutein (2), zeaxanthin [(3/ , 37 )-3,p-carotene-3,3 -diol] (15), and, finally, to violaxanthin (3) (Fig. 26.10) (Britton, 1993). Labeling studies have shown that hydroxyla-tions such as those involved in the conversion of zeaxanthin and lutein are formed by the direct replacement of the hydrogen by OH (Britton, 1993). 

There are two principal mechanisms for the introduction of a cis double bond into a hydrocarbon chain, the anaerobic and the aerobic mechanisms. 

Microbial Biofllms and the Interactions Between Aerobic and Anaerobic Populations In the preceding discussion, the mechanisms of microbial corrosion have been divided in the traditional way into anaerobic and aerobic mechanisms, which refer to the living conditions of the microorganisms involved in the... 

Bacteria are single-cell microorganisms, which are rod, cocci, and spiral shaped, whereas a few are chain like and filamentous in shape. The bacterial species cannot have aerobic/anaerobic respiration, whereas fungi need aerobic mechanisms (Doi and Abe, 1990). Usually, bacteria are motile and non-cholorophyllous. 

The biosynthesis of unsaturated fatty acids can use anaerobic or aerobic mechanisms... 

Once fatty acids have been made de novo they can either be modified by elongation (above), by desaturation or by other reactions. Desaturation usually takes place by an aerobic mechanism - an exception being in the E. coli fatty acid synthetase. Aerobic desaturases differ from each other by the nature of the acyl substrate they use, the type of reduced cofactor and the position at which the double bond is introduced into the acyl chain. Particularly notable are the desaturases which produce the polyunsaturated linoleic and a-linolenic acids. These enzymes use complex lipid substrates rather than acyl-thioesters. 

The function of aeration in a wastewater treatment system is to maintain an aerobic condition. Water, upon exposure to air, tends to estabUsh an equihbrium concentration of dissolved oxygen (DO). Oxygen absorption is controlled by gas solubiUty and diffusion at the gas—hquid interface. Mechanical or artificial aeration may be utilised to speed up this process. Agitating the water, creating drops or a thin layer, or bubbling air through water speeds up absorption because each increases the surface area at the interface. 

Biodegradation. The biodegradation properties of various organics are shown in Table 13. The mechanism of aerobic degradation is shown in... 

For aeration, diffused-air or mechanical units are used. Air diffusers are commonly used ia North America, but some mechanical aeration units are iastalled ia plants with capacities >3, 800 /d (10 gal/d). Aeration transfers oxygen to the sewage and maintains aerobic conditions, mixes sewage and floe, and keeps the floe ia suspension. 

Metabolic rate (M) The rate of transformation of chemical energy into heat and mechanical work by aerobic and anaerobic metabolic activities w ithin an organism, usually expressed per unit area of the total body surface, in met or W m -. 

Iron-Oxidizing Bacteria. These are aerobic organisms capable of growing in systems with less than 0.5 ppm oxygen. They oxidize iron from ferrous to the ferric state by the following mechanism ... 

Mechanism and sulphur oxidation Apart from its intrinsic interest the economic importance of acid corrosion and more lately interest in ore leaching, has stimulated considerable work on the oxidation of sulphur, Fe and Mn. It must be stressed that the Thiobacilli are obligate aerobes, i.e. that depend on molecular oxygen as a terminal electron acceptor. Possible reactions for the oxidation of sulphur are... 

Organisms also evolved powerful detoxifying mechanisms that remove toxic materials or convert them to non-toxic forms or nutrients. Examples of alterations to non-toxic forms are the conversions of hydrogen sulfide to sulfate and nitrite to nitrate. The prime example of development of the ability to use a toxic substance is the evolution of aerobic metabolism, which converted a serious and widespread toxin, oxygen, into a major resource. This development, as we have seen, greatly increased the productivity of the biosphere and generated the oxygen-rich atmosphere of today s Earth. 

Two major types of muscle fibers are found in humans white (anaerobic) and red (aerobic). The former are particularly used in sprints and the latter in prolonged aerobic exercise. During a sprint, muscle uses creatine phosphate and glycolysis as energy sources in the marathon, oxidation of fatty acids is of major importance during the later phases. Nonmuscle cells perform various types of mechanical work carried out by the structures constituting the cytoskeleton. These strucmres include actin filaments (microfilaments), micrombules (composed primarily of a- mbulin and p-mbulin), and intermediate filaments. The latter include keratins, vimentin-like proteins, neurofilaments, and lamins. 

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