Respiratory metabolism

Ethylene coordinates the expression of genes responsible for enhanced respiratory metabolism, chlorophyll degradation, carotenoid synthesis, conversion of starch to sugars, increased activity of cell wall-degrading enzymes, aroma volatile production, and so on. All these events stimulate a series of biochemical, physiological, and structural changes making fruits mature and attractive to the consumer. 

PJ Dunphy, AF Brodie. The structure and function of quinones in respiratory metabolism. Meth En-zymol 18C 407-461, 1971. 

Under aerobic conditions, the glycolytic pathway becomes the initial phase of glucose catabolism (fig. 13.2). The other three components of respiratory metabolism are the tricarboxylic acid (TCA) cycle, which is responsible for further oxidation of pyruvate, the electron-transport chain, which is required for the reoxidation of coenzyme molecules at the expense of molecular oxygen, and the oxidative phosphorylation of ADP to ATP, which is driven by a proton gradient generated in the process of electron transport. Overall, this leads to the potential formation of approximately 30 molecules of ATP per molecule of glucose in the typical eukaryotic cell. 

The components of respiratory metabolism include glycolysis, the tricarboxylic acid (TCA) cycle, the electron-transport chain, and the oxidative phosphorylation of ADP to ATP. Glycolysis converts glucose to pyruvate the TCA cycle fully oxidizes the pyruvate (by means of acetyl-CoA) to C02 by transferring electrons stepwise to... 

Duthie, G.G. (1982). The respiratory metabolism of temperature-adapted flatfish at rest and during swimming activity and the use of anaerobic metabolism at moderate swimming speeds. Journal of Experimental Biology 9,359-373. 

Tolerance of the fruit to anoxia is evidenced by the maintenance of a high energy charge (an index of the cell energy status), very close to that of berries in air for 4-7 days. In addition, mitochondria retain much of their ability to return to respiratory metabolism on exposure to air after... 

Sherry wines are obtained from young wines, carefully selected soon after completing fermentation. These are typically fortified by adding vinous alcohol until they reach an alcohol content of 15-15.5°. They are subsequently transferred to oak barrels before being aged. In most sherries, wine aging occurs in the so-called solera and criaderas system under the flor film of yeast. Once alcoholic fermentation is finished, races of Saccharomyces cerevisiae that can grow on the surface of the wine switch from fermentative to oxidative (respiratory) metabolism. They spontaneously form a biofilm called flor on the wine surface. 

The theoretical background concerning regulation of fluxes through metabolic pathways, the identification of regulatory points and the mechanisms whereby different catabolic and synthetic pathways are integrated has been expertly covered by Barrett (39). Earlier reviews of the regulation of respiratory metabolism in cestodes are those of Bryant (99, 100). 

Cestodes produce a range of end-products as a result of their respiratory metabolism (Table 5.4). Bryant Flockhart (104) have usefully divided the patterns of respiratory metabolism among parasitic helminths into three types. The metabolism of larval and adult cestodes fits broadly into the first two categories of this biochemical classification and these are illustrated in Fig. 5.4. Type 1 contains the homolactate fermenters in which carbohydrate is degraded, via glycolysis, to lactate and excreted. The ANU (Australian) strain of H. diminuta tends towards this type of metabolism (see below). 

Type 3 fermentation, characterised by a series of reactions between mitochondrial end-products that yield branched-chain fatty acids (e.g. 2-methylvalerate, 2-methylbutyrate), occurs in Ascaris, a number of other intestinal nematodes and in some trematodes (490). However, cestodes, with the exception of Bothriocephalus scorpii, which excretes methyl-butyrate (107), have not been shown to produce branched-chain fatty acids as end-products of respiratory metabolism. Some or all of the enzymes of the TCA cycle may be present in cestodes in addition to the type 1 and type 2 fermentation pathways. The extent to which the cycle may contribute to carbohydrate metabolism in cestodes is considered below. 

It is generally accepted that H. dimimta excretes lactate, succinate and acetate as its major respiratory end-products (apart from C02) and recent nuclear magnetic resonance (n.m.r.) analysis (Fig. 5.6) (62,83) has confirmed earlier data obtained by more conventional approaches. There is, however, less agreement as to the precise quantity of each end-product excreted by this worm and how its respiratory metabolism is regulated. 

The key position of malic enzyme, which oxidatively decarboxylates malate to pyruvate inside the mitochondrion, in cestode respiratory metabolism has been discussed above. The malic enzyme of H. diminuta has been most investigated (221,... 

Carbon dioxide utilisation, and the regulation of respiratory metabolic pathways in parasitic helminths. Advances in Parasitology, 13 35-69. 

Bryant, C. Behm, C. A. (1976). Regulation of respiratory metabolism in Moniezia expansa under aerobic and anaerobic conditions. In Biochemistry of parasites and host-parasite relationships, ed. H. Van den Bossche, pp. 89-94. North-Holland Publishing Co. Amsterdam. 

Investigation on the respiratory metabolism of eggs and coracidia of Diphyllobothrium latum (L.) Cestoda. Bulletin de I Academie Polonaise des Sciences. Cl.II, Serie des Sciences Biologiques, 12 29-34. 

Increase followed by decrease of respiratory metabolism and of pentose-cycle. 

Kobayashi M, Matsuo Y, Takimoto A, Suzuki S, Maruo F, Shoun H (1996) Denitrification, a novel type of respiratory metabolism in fungal mitochondrion. J Biol Chem 271 16263-16267... 

Hase, A., Changes in respiratory metabolism during callus growth and adventitious root formation in Jerusalem artichoke tuber tissues, Plant Cell Physiol., 28, 833-841, 1987. 

Deposition of elemental sulphur formed from sulphate Essential collaboration of at least two different microbial species occurs in the transformation of sulphate to S° in salt domes or similar sedimentary formations (see Ivanov, 1968). This transformation is dependent on the interaction of a sulphate reducer like Desulfovibrio desulfuricans, which transforms sulphate to H2S in its anaerobic respiratory metabolism, and an H2S oxidizer like Thiobacillus thioparus, which, under conditions of limited O2 availability, transforms H2S to S° in its respiratory metabolism (van den Ende van Gemerden, 1993). The collaboration of these two physiological types of bacteria is obligatory in forming S° from sulphate because sulphate reducers cannot form S° from sulphate, even as a metabolic intermediate. It should be noted, however, that the sulphate reducers and H2S oxidizers are able to live completely independent of each other as long as the overall formation of S° from sulphate is not a requirement. 

Cytochrome c oxidase, the terminal oxidase in the respiratory metabolism of all aerobic organisms, plants, animals, yeasts, algae, and some bacteria, is responsible for catalyzing the reduction of dioxygen to water. 

The biological aging of wines has aroused increasing interest in recent years, as reflected in the large number of papers on this topic over the last decade. Biological aging in wine is carried out by flor yeasts. Once alcoholic fermentation has finished, some Saccharomyces cerevisiae yeast races present in wine switch from a fermentative metabolism to an oxidative (respiratory metabolism) and spontaneously form a biofllm called flor on the wine surface. Wine under flor is subject to special conditions by effect of oxidative metabolism by yeasts and of the reductive medium established as they consume oxygen present in the wine. These conditions facilitate... 

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