Energy metabolism acetate

Fluoroacetate produces its toxic action by inhibiting the citric acid cycle. The fluorine-substituted acetate is metabolized to fluoroci-trate that inhibits the conversion of citrate to isocitrate. There is an accumulation of large quantities of citrate in the tissue, and the cycle is blocked. The heart and central nervous system are the most critical tissues involved in poisoning by a general inhibition of oxidative energy metabolism. ... 

The only metabolic activity that has been for decades ascribed to the trichomonad hydrogenosome was related to energy metabolism. It has been unequivocally shown that, under anaerobic conditions, isolated intact hydrogenosomes produced roughly equimolar amounts of acetate, CO2, and hydrogen from pyruvate in a process accompanied by substrate-level phos-... 

The enzyme is present in large amounts in acetogenic bacteria, where it is involved in an unusual pathway for fixation of C02 with the formation of acetate (25,26). In acetogens this reaction is involved both in production of energy, with acetate as a waste product, and in biosynthesis of cell constituents starting from acetate. CO oxidoreductase is also present in methanogenic bacteria, where it is used in biosynthetic metabolism (25, 27). 

Parasitic stages, on the other hand, generally do not use oxygen as the final electron acceptor but use fermentative processes to obtain most of their ATP. For these stages, an uneconomical energy metabolism is not detrimental, as the host provides the nutrients. Most adult flatworms inside the final host produce end products of a fermentative carbohydrate breakdown, such as succinate, acetate, propionate and lactate. These end products are formed via malate dismutation, a fermentative pathway, which is present in all types of parasitic worms (flatworms as well as many nematodes), but which is also present in animals like freshwater snails, mussels, oysters and other marine organisms. Malate dismutation is linked to a specially... 

Van Vugt, F., van derMeer, P. and van den Bergh, S.G. (1979) The formation of propionate and acetate as terminal processes in the energy metabolism of the adult liver fluke Fasciola hepatica. International Journal of Biochemistry 10, 11-18. 

This is a noncyclic pathway that also results in the fixation of two molecules of C02 to form acetyl-CoA. It was elucidated by Wood, Ljungdahl, Thauer and others as a pathway which is used by acetogenic bacteria to synthesize acetate from C02 in their energy metabolism [21]. The acetyl-CoA pathway resembles the Monsanto process of acetate synthesis from CO and methanol, with one molecule of C02 being reduced to the level of methyltetrahydropterin, while another C02 molecule is reduced to the level of carbon monoxide in the reaction catalyzed by the nickel-dependent carbon monoxide dehydrogenase (Figure 3.3). 

Fig. 5.4. Two types of energy metabolism in cestodes. (a) Type 1 homolactate fermentation, (b) Type 2 Malate dismutation. Reaction 3 involves a carboxylation step decarboxylation occurs at 6, 7 and 10. Reducing equivalents are generated at reactions 6 and 7 one reducing equivalent is used at reaction 9. Thus, when the mitochondrial compartment is in redox balance and malate is the sole substrate, twice as much propionate as acetate is produced. Key 1, pyruvate kinase 2, lactate dehydrogenase 3, phosphoenolpyruvate carboxykinase 4, malate dehydrogenase 5, mitochondrial membrane 6 malic enzyme 7, pyruvate dehydrogenase complex 8, fumarase 9, fumarate reductase 10, succinate decarboxylase complex. indicates reactions at which ATP is synthesised from ADP cyt, cytosol mit, mitochondrion. (After Bryant Flockhart, 1986.)...

Fig. 7.5. Pyruvatetformate lyase (PFL) and not pyruvatetferredoxin oxidoreductase (PFO) is the key enzyme in the hydrogenosomal energy metabolism of the anaerobic chytrid of Piromyces sp. E2 (Akhmanova et al. 1999 Boxma et al. 2004). Hydrogen formation depends solely on malate it can become marginal under certain metabolic conditions. The relative fluxes through the pathways are indicated by the thickness of the arrows, which are proportional to the calculated fluxes in the presence of 0.3% fructose. Use of PFL instead of PFO allows the formation of reduced equivalents to be avoided. Consequently, chytrid hydrogenosomes excrete formate and acetate as end products of their energy metabolism. (From Boxma et al. 2004)...

Transformation by a single microbial species Some geomicrobial transformations in nature involve a single microbial species. An example of such a transformation is the anaerobic reduction of a Mn(IV) oxide to Mn " " by S. oneidensis or G. metallireducens in an environment with a plentiful supply of an appropriate electron donor like lactate for S. oneidensis or acetate for G. metallireducens. Because each of these two microbial species can perform the reduction by themselves, and because electron donors like lactate and acetate are formed as major end-products in the energy metabolism of a variety of microbes present in the same environment that harbours S. oneidensis or G. metallireducens, the latter do not need to form specific microbial associations to bring about Mn(IV) oxide reduction. 

Hosoi, R., Okada, M., Hatazawa, J., Gee, A., Inoue, O. (2004). Effect of astroc 4ic energy metabolism depressant on 14C-acetate uptake in intact rat brain. Cereb. Blood Flow Metab. 24 188-90. 

Several reactions of CO2 reduction to CH4 by methanogens resemble those of CO2 reduction to by acetogens. Most acetogens, which are anaerobic bacteria (eubacteria), catalyze in their energy metabolism the formation of acetate from CO2 and H2 according to the following equation ... 

The primary fate of dietary fibers is digestion and catabolism by the gut microflora to short-chain fatty acids and carbon dioxide. The major products of this microbial metabolism — acetic, propionic, and butyric acid — are important sources of energy for ruminants (sheep, cows). Dietary fiber is retained in a chamber of their gastrointestinal tracts, called the rumen, where it is converted to short-chain fatty acids by the gut microflora. The fatty acids produced may supply 35-75% of the energy requirement of the ruminant. 

The filamentous sulfur bacteria, Thioploca, oxidize sulfide with nitrate in their energy metabolism. Alternatively, they can assimilate CO or acetate as a carbon source. What kind(s) of -troph is Thioploca (use Table 5.3 and 5.4). 

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