Energy yield

The uniqueness of propionic acid fermentation is due to the participation of PEP carboxytransphosphorylase, the enzyme not found in the other organisms that synthesize propionate. Due to the presence of this enzyme the propionic acid fermentation functions as a cyclic process (for the significance of cycling, see above). Another peculiarity of this fermentation is related to the way propionate is formed, which is coupled with the 

Three moles of ATP are derived from 1.5 moles of glucose in the course of glycolysis. Then one those (pyruvate) is oxidized to CO2 and acetyl-P, and acetate and ATP are formed from the latter in the presence of ADP and acetyl kinase. Two other molecules of pyruvate enter the cycle. Cytochrome b is involved in the anaerobic transport of two electrons from NADH to fumarate (Cox et al., 1970), and 2 moles of ATP are formed by oxidative phosphorylation (Van Gent-Ruijters et al., 1975). If two electrons are transported from lactate or glycerol-3-phosphate to fumarate, the formation of 1 mole of ATP is postulated. 

Apart from the fermentation, other processes are known, which may contribute to the apparent high ATP yields in propionibacteria. For instance, translocation of a metabolite, if coupled with transmembrane proton movements, can significantly augment the protonmotive force that drives the ATP synthesis, e.g., lactate efflux in a symport with protons in lactic acid bacteria. 

The mechanisms discussed above may also operate in the propionibacteria, which are capable of decarboxylating methylmalonyl-CoA and are highly tolerant to NaCl. Theoretically, the decarboxylation of 2 moles of methylmalonyl-CoA will yield 2/3 mole of ATP. Therefore, 1.5 moles of glucose can yield as much as 6 moles of ATP, which is consistent with the ATP yields calculated on the basis of the molar Tatp and 7s coefficients. In P. freudenreichii the 7atp coefficient varies in the range of 15.5-16.9 g dry weight per mol ATP under anaerobic conditions (De Vries et al., 1973 Pritchard et al., 1977). 

A direct determination of the ATP content in P. shermanii at different growth phases (Gaitan and Vorobjeva, 1981) was carried out using the luciferin-luciferase method (Strehler and McElroy, 1957) with immobilized luciferase (Brovko et al., 1978). In cells growing on glucose the ATP level increased continuously up to 5 nmol per mg dry weight (Fig. 3.3). The ATP level dropped toward the end of the log-phase, but remained above 4 nmol/mg. The decrease was most prominent in the mid-log phase in the stationary phase the ATP level stabilized. The decline in ATP levels was accompanied by the accumulation of polyphosphates (Gaitan and Vorobjeva, 1981). 

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Equation (ASA. 110) represents the canonical fonn T= constant) of the variational theory. Minimization at constant energy yields the analogous microcanonical version. It is clear that, in general, this is only an approximation to the general theory, although this point has sometimes been overlooked. One may also define a free energy... 

In contrast with electrorefining, there is a minimum cell voltage of ca 1.67 V, below which there is no appreciable current flow. Hence, the energy yield is only ca 0.3 kg of copper per kilowatt hour, as contrasted with about 3 kg/kWh for electrorefining. 

Energy can almost always be replaced in part by other inputs. For example, a steam pipe can be insulated more heavily or an industrial process can be modified to use more labor and less energy. Economic efficiency docs not imply minimizing the use of energy or any other input, but rather finding the appropriate mix of inputs. The economically efficient level of inputs is reached when the last dollar spent on energy yields the same amount of benefits as the last dollar spent on labor or materials or any other input. 

American nuclear chemist Glenn Seaborg s team of experimenters isolates plutonium, which proves to be a better fuel for nuclear reactors than uranium because of its greater energy yield. 

The temperature derivative of the free energy yields an expression for the entropy change occuring during the cell reaction... 

Nitrification consists of two energy yielding steps the oxidation of ammonium to nitrite, and the oxidation of nitrite to nitrate. These equations are generally represented as follows ... 

Probe methods like particle insertion and test particle methods (29-32) are quite useful for computing chemical potentials of constituent particles in systems with low densities. Test particles are randomly inserted the average Boltzmann factor of the insertion energy yields the free energy. For dense systems these methods work poorly because of the poor statistics obtained. 

Four of the B vitamins are essential in the citric acid cycle and therefore in energy-yielding metabolism (1) riboflavin, in the form of flavin adenine dinucleotide (FAD), a cofactor in the a-ketoglutarate dehydrogenase complex and in succinate dehydrogenase (2) niacin, in the form of nicotinamide adenine dinucleotide (NAD),... 

In most tissues, where the primary role of the citric acid cycle is in energy-yielding metabohsm, respiratory control via the respiratory chain and oxidative phosphorylation regulates citric acid cycle activity (Chapter 14). Thus, activity is immediately dependent on the supply of NAD, which in turn, because of the tight couphng between oxidation and phosphorylation, is dependent on the availabihty of ADP and hence, ulti-... 

Table 27-1. Energy yields, oxygen consumption, and carbon dioxide production in the oxidation of metabolic fuels.

Ten Percent of the Energy Yield of a Meal May Be Expended in Forming Reserves... 

Thiamin has a central role in energy-yielding metabo-hsm, and especially the metabohsm of carbohydrate (Figure 45-9). Thiamin diphosphate is the coenzyme for three multi-enzyme complexes that catalyze oxidative decarboxylation reactions pymvate dehydrogenase in carbohydrate metabolism a-ketoglutarate dehydro-... 

ViTAMiN B2 (RiBOFLAViN) HAS A CENTRAL ROLE iN ENERGY-YIELDING METABOLISM... 

A (fake) potential energy, yielding the equation of motion (A.l), is (cf. the discussion of surface waves on a spherical liquid droplet in Landau adn Lifshitz [116]) ... 

Increased production of enzymes required for energy-yielding reactions and for synthesis of RNA and proteins... 

Energy-yielding reactions and energy-storage systems form a common pattern found in all hving systems and may be depicted thus ... 

PN should provide a balanced nutritional intake, including macronutrients, micronutrients, and fluid. Macronutrients, including amino acids, dextrose, and intravenous lipid emulsions, are important sources of structural and energy-yielding substrates. A balanced PN formulation includes 10% to 20% of total daily calories from amino acids, 50% to 60% of total daily calories from dextrose, and 20% to 30% of total daily calories from intravenous lipid emulsion. Micronutrients, including electrolytes, vitamins, and trace elements, are required to support essential biochemical reactions. Parenteral... 

A quasichemical theory, using ab initio simulation (rPBE functional) to generate data for the computation of the various contributions to the free energy, yields an estimate for the excess chemical potential of water very close to the experimental value. 

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