Anaerobic end products

Fermentation, or the partial (02 independent) catabolism of substrates to anaerobic end products, is a second means of forming ATP. In animals, the commonest fermentative pathway is that of anaerobic glycolysis (figure 2.1). At high pH (> 8.0), the summed reaction can be written as follows ... 

In true fermentation, the free energy drop between substrate (say glucose) and anaerobic end products is always modest by comparison with respiration, because fermentation is never based on electron transfer chains coupled to phosphorylation. Rather, true fermentations depend upon a variety of oxidation-reduction reactions involving organic compounds, C02, molecular hydrogen, or sulfur compounds. All these reactions are inefficient in terms of energy yield (moles ATP per mole substrate fermented), and, therefore, the mass of cells obtainable per mole of substrate is much smaller than with respiratory-dependent species. 

The standard hallmark of fermentation is the accumulation of partially metabolized anaerobic end products. This is an inefficient metabolic strategy because a lot of potential chemical energy is still retained in the end products being formed moreover, these are often noxious and therefore at high levels may well... 

Under anaerobic conditions procyclic stages of T. rhodesiense are capable of utilizing glucose and glycerol, provided COj is present (8). Most of the carbon is recovered as succinate (75 and 63%, respectively) and a smaller amount of acetate (25 and 4%, respectively). Anaerobic data for T. brucei are not available. The glycosomal phospho-enolpyruvate carboxykinase (PEPCK) and malate dehydrogenase, virtually absent from bloodstream forms, but fully expressed in the procyclics, are believed to fix COj and produce succinate as an anaerobic end-product (4,10). 

Respiration, or biological oxidation, is the use of oxygen as an electron receptor in the cataboHc degradation of an organic and can occur either aerobically or anaerobically. Aerobic respiration uses free oxygen as an electron receptor whereas anaerobic respiration uses inorganic oxygen. In both cases, however, water and carbon dioxide are the principal end products. 

Anaerobic treatment is usually employed for high strength wastewaters. In anaerobic treatment, complex organics are broken down through a sequence of reactions to end products of methane gas, CH, and carbon dioxide, CO2 ... 

The primary advantage of aerobic digestion is that it produces a biologically stable end product suitable for subsequent treatment in a variety of processes. Volatile solids reductions similar to anaerobic digestion are possible. Some parameters affecting the aerobic digestion process are ... 

Anaerobic utilisation of carbohydrates is strongly inhibited by the end product ethanol, giving low yield coefficients compared to aerobic utilisation. 

Microorganisms under anaerobic growth conditions have the ability to utilise glucose by the Embden-Mereyhof-Parnas pathway.4 Carbohydrates are phosphorylated through the metabolic pathway the end products are two moles of ethanol and carbon dioxide.5... 

Bowlus, R.D. Somero, G.N. (1979). Solute compatibility with enzyme function and structure rationales for the selection of osmotic agents and end products of anaerobic metabolism in marine invertebrates. Journal of Experimental Zoology, 208, 137-52. 

Glucose is metabolized to pyruvate by the pathway of glycolysis, which can occur anaerobically (in the absence of oxygen), when the end product is lactate. Aerobic tissues metabolize pyruvate to acetyl-CoA, which can enter the citric acid cycle for complete oxidation to CO2 and HjO, linked to the formation of ATP in the process of oxidative phosphorylation (Figure 16-2). Glucose is the major fuel of most tissues. 

Lactate is the end product of glycolysis under anaerobic conditions (eg, in exercising muscle) or when the metabolic machinery is absent for the further oxidation of pyruvate (eg, in erythrocytes). 

As for the aerobic degradation of pyridines, hydroxylation of the heterocyclic ring is a key reaction in the anaerobic degradation of azaarenes by Clostridia. Whereas in Clostridium barkeri, the end products are carboxylic acids, CO2, and ammonium, the anaerobic sulfate-reducing Desulfococcus niacinii degraded nicotinate completely to CO2 (Imhoff-Stuckle and Pfennig 1983), although the details of the pathway remain incompletely resolved. 

Laboratory studies have provided inconsistent results regarding the degree to which MTBE is biodegraded anaerobically to end products and the extent to which other oxygenates are biodegraded under anaerobic conditions. 

---