Oxygen consuming systems

Other Reducing-Equivalent Transport and Oxygen-Consuming Systems... 

Recently, it has been shown (Iordan and Petukhova, 1995) that the AdoCbl-independent RNR (metal-, probably manganese-dependent) is a molecular oxygen-consuming system (cf Fig. 5.12), different from AdoCbl-dependent enzymes that function in the absence of air, but similar to mammalian RNRs that also require oxygen (Probst et al., 1989). 

The minimum oxygen utihsation rate is xjjbnvJY0l. If the system is mass-transfer limited, C, approaches zero. Then the amount of oxygen absorbed is exactly equal to the amount of oxygen consumed. Equation (3.11.8) leads to the following ... 

Active transport is of basic importance for life processes. For example, it consumes 30-40 per cent of the metabolic energy in the human body. The nervous system, which constitutes only 2 per cent of the weight of the organism, utilizes 20 per cent of the total amount of oxygen consumed in respiration to produce energy for active transport. 

The versatility and accuracy of the oxygen consumption method in heat release measurement was demonstrated. The critical measurements include flow rates and species concentrations. Some assumptions need to be invoked about (a) heat release per unit oxygen consumed and (b) chemical expansion factor, when flow rate into the system is not known. Errors in these assumptions are acceptable. As shown, the oxygen consumption method can be applied successfully in a fire endurance test to obtain heat release rates. Heat release rates can be useful for evaluating the performance of assemblies and can provide measures of heat contribution by the assemblies. The implementation of the heat release rate measurement in fire endurance testing depends on the design of the furnace. If the furnace has a stack or duct system in which gas flow and species concentrations can be measured, the calorimetry method is feasible. The information obtained can be useful in understanding the fire environment in which assemblies are tested. 

An oxygen pipeline system was established in western Europe in the Iate-1970s that is 592 miles (956 kilometers) long. The Eastern Network of this system serves 30 consumers in France, Luxembourg, and West Germany the Northern Network serves some 40 additional users in France, Belgium, and the Netherlands. 

The entrained systems are generally high oxygen consumers - almost double the requirement for the fixed bed units. Energy for oxygen production could be recovered from hot gasifier effluent gases if suitable waste heat boilers and superheaters can be developed. 

A reaction associated with nonphosphorylating oxygenases is shown in Reaction 4, an example of a minor oxygen-consuming reaction in biological systems. The oxygen consumption by cytochrome P-450 occurs in the microsomes of animals and the microbodies of plants. 

Both groups of reactions are found in bacteria (14), all higher animals (i5), and plants (16) however, oxidative phosphorylation is responsible for 90 % of the oxygen consumed (i 7). Oxidative phosphorylation is driven by the respiratory electron-transport system that is embedded in the lipoprotein inner membrane of eukaryotic mitochondria and in the cell membrane of prokaryotes. It consists of four complexes (Scheme I). The first is composed of nicotinamide adenine dinucleotide (NADH) oxidase, flavin mononucleotide (FMN), and nonheme iron-sulfur proteins 18,19), and it transfers electrons from NADH to ubiquinone. The second is composed of succinate dehydrogenase (SDH), flavin adenine dinucleotide (FAD), and nonheme iron-sulfur proteins (20), and it transfers electrons from succinate to ubiquinone 21, 22). The third is composed of cytochromes b and c, and nonheme iron-sulfur proteins (23), and it transfers electrons from ubiquinone (UQ) to cytochrome c 24). The fourth complex consists of cytochrome c oxidase [ferrocytochrome c 0 oxidoreductase EC 1.9.3.1 25)] which transfers electrons from cytochrome c to O2 26, 27). 

This instrument measures the oxygen consumed by a sample exposed to rapid pyrolysis temperature profiles, thus measuring the heat release (HR) capacity as well as the total heat evolved from the sample. The instrument measures the inherent flammability of a polymeric material the lower the HR capacity and total heat, the less flammable the material. The PCFC results obtained from the BPC polycarbonate show a much lower heat release capacity and also a much higher char yield, compared with traditional BPA polycarbonate, thereby underscoring the effectiveness of the BPC system. 

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