Dismutation energy

The dismutation (disproportioning) of two free radicals is accompanied by release of a portion of reaction energy as a light quantum. As the quantum yield of such a process is extremely low, the detection of this type of chemiluminescence is technically complicated. Several compounds like lucigenin and luminol have a high quantum yield after reaction with peroxide radicals. Therefore, they are widely used for the detection of these radicals, particularly in the examination of phagocyting cells. 

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... 

The rate of electron transfer that occurs to/from the metal center is high. Structure based modeling of the active site of human MnSOD [40], which includes calculating the energies of both the oxidized and reduced states with either water or hydroxide bound to the metal, suggests the rate of this internal electron transfer is enhanced by electron-relaxation effects. In addition, a 0.17 V redox potential is calculated, a value that is low compared with the experimental values of 0.31 V fori . coli and 0.26 V for B. stearothermophilus, respectively. A potential of —0.30 V seems to be optimal as it lies midway between the redox potentials of the two half reactions of the dismutation process [41],... 

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.)...

It is likely that pyruvate, the product of the oxidative branch of the mitochondrial dismutation reaction, is further metabolised in cestodes to acetyl-CoA by oxidation with NAD+, as catalysed by the lipoamide-dependent mitochondrial pyruvate dehydrogenase complex. This enzyme has been reported in H. diminuta (935) and S. solidus (406). The acetyl-CoA is then hydrolysed to acetate. During this step, ATP synthesis may occur through the conservation of the acetyl-CoA energy-rich thioester bond by the combined action of an acyl-CoA transferase and a thiokinase (398) as follows ... 

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