Aerobic metabolism production

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. 

However, the many pathways by which MTBE and other oxygenates may be biodegraded anaerobically have been the subject of recent research and ongoing studies. Table 24.12 highlights the various electron acceptors that are used in anaerobic bioremediation studies and contrasts the products of complete anaerobic degradation with those for aerobic metabolism. 

The final product of the aerobic metabolic pathway of chloroform is carbon dioxide (Brown et al. 1974a Fry et al. 1972). This carbon dioxide is mostly eliminated through the lungs, but some is incorporated into... 

Biochemical reactions include several types of decarboxylation reactions as shown in Eqs. (1)-(5), because the final product of aerobic metabolism is carbon dioxide. Amino acids result in amines, pyruvic acid and other a-keto acids form the corresponding aldehydes and carboxylic acids, depending on the cooperating coenzymes. Malonyl-CoA and its derivatives are decarboxylated to acyl-CoA. -Keto carboxylic acids, and their precursors (for example, the corresponding hydroxy acids) also liberate carbon dioxide under mild reaction conditions. 

Waste Microbes International, Inc. (WMI) has a series of bacterial cultures designed to augment aerobic metabolism of petroleum products and other contaminants. The WMI-2000 is a blend... 

Dinitrobenzene, which is used widely in the production of pesticides and dyes, causes testicular cancer in the rat. The compound displays the prototypical aerobic metabolism of the nitroaromatics, namely bioreduction to a radical anion, followed by electron transfer to oxygen ... 

Because of the interest in the potential biological applications of complexes containing coordinated dioxygen, and the importance of superoxides as a by-product of aerobic metabolic processes, aqueous stud-... 

The existence of mitochondrial DNA, ribosomes, and tRNAs supports the hypothesis of the endosymbiotic origin of mitochondria (see Fig. 1-36), which holds that the first organisms capable of aerobic metabolism, including respiration-linked ATP production, were prokaryotes. Primitive eukaryotes that lived anaerobically (by fermentation) acquired the ability to carry out oxidative phosphorylation when they established a symbiotic relationship with bacteria living in their cytosol. After much evolution and the movement of many bacterial genes into the nucleus of the host eukaryote, the endosymbiotic bacteria eventually became mitochondria. 

The biochemical importance of flavin coenzymes ap-pears to be their versatility in mediating a variety of redox processes, including electron transfer and the activation of molecular oxygen for oxygenation reactions. An especially important manifestation of their redox versatility is their ability to serve as the switch point from the two-electron processes, which predominate in cytosolic carbon metabo-lism, to the one-electron transfer processes, which predomi-nate in membrane-associated terminal electron-transfer pathways. In mammalian cells, for example, the end products of the aerobic metabolism of glucose are C02 and NADH (see chapter 13). The terminal electron-transfer pathway is a membrane-bound system of cytochromes, nonheme iron proteins, and copper-heme proteins—all one-electron acceptors that transfer electrons ultimately to 02 to produce H20 and NAD+ with the concomitant production of ATP from ADP and P . The interaction of NADH with this pathway is mediated by NADH dehydrogenase, a flavoprotein that couples the two-electron oxidation of NADH with the one-electron reductive processes of the membrane. 

Neither NO nor HNO is appreciably cytotoxic under anaerobic conditions (135). Even in the presence of 02 the free radical NO protects against peroxide and 02 toxicity, suggesting that in vitro production of RNOS from NO is of lesser importance than the presence of NO itself. The question arises as to whether the enhanced toxicity of HNO in the presence of 02 or peroxides is a function solely of inhibition of the peroxide consuming capacity of cells for instance by depletion of GSH (Eq. 21) or if RNOS are involved. It is also possible that aerobic metabolism primes the cell for HNO toxicity in some fashion. 

If DMS concentrations at the surface of the ocean are presumed to be at steady state, production must balance loss. The fate of DMS is thought to be evasion across the sea surface into the marine atmospheric boundary layer. However, since rates of DMS production are unknown, it is impossible to compare production with flux to the atmosphere, which is relatively well constrained. An alternative sink for DMS in seawater is microbial consumption. The ability of bacteria to metabolize DMS in anaerobic environments is well documented (32-341. Data for aerobic metabolism of DMS are fewer (there are at present none for marine bacteria), but Sivela and Sundman (25) and de Bont et al. (25) have described non-marine aerobic bacteria which utilize DMS as their sole source of carbon. It is likely that bacterial turnover of DMS plays a major role in the DMS cycle in seawater. 

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