Metabolism of sugars

Aerobic living features metabolize sugars and fatty acids to carbon dioxide. Accordingly, there are some kinds of decarboxylation reactions. TPP-mediated decarboxylation of pyruvic acid to acetaldehyde is one of the most important steps of the metabolism of sugar compounds (Fig. 1). When the intermediate reacts with lipoic acid instead of a proton, pyruvic acid is converted to acetylcoenzyme A, which is introduced to TCA cycle (Fig. 2). 

S glycerol 3-phosphate -h D-glucose <1> (<1> involved in anaerobic metabolism of sugars in bloodstream trypanosomes [1]) (Reversibility <1>... 

Thompson, J. D., Turner, K. W. and Thomas, T. D. 1978. Catabolite inhibition and sequential metabolism of sugars by Streptococcus lactis. J. BacterioL 133, 1163-1174. 

Enolose. A key reaction in the metabolism of sugars is the dehydration of 2-phosphoglycerate to form phosphoenolpyruvate (PEP), the phospho derivative of the enolic form of pyruvic acid ... 

Metabolism of sugars often involves dehydration to a,P-unsaturated carbonyl compounds. An example is the formation of 2-oxo-3-deoxy derivatives of sugar acids (Eq. 14-36). Sometimes a carbonyl group is... 

Neurons synthesize acetylcholine from choline, which is obtained from the diet, and from acetyl groups that originate in mitochondria from the metabolism of sugar. Here is yet another example of the importance of sugar for your brain s normal function. The synthesis of acetylcholine occurs within the cytoplasm of your neurons, and the product is stored in synaptic vesicles, those small round packets that neurons release to communicate with each other. Neurons pay a lot of attention to the shelf life of their neurotransmitters they prefer to release the most recently produced neurotransmitter molecules first. As you can see, neurons do not behave like your local grocer they do... 

A reaction involved in the metabolism of sugars is the splitting of fructose- 1,6-diphosphate to give glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. In the living system, this retro-aldol is catalyzed by an enzyme called aldolase however, it can also be catalyzed by a mild base. Propose a mechanism for the base-catalyzed reaction. 

Pimentel, M. S., Silva, M. H., Cortes, I., and Faia, A. M. 1994. Growth and metabolism of sugar and acids of Leuconostoc oenos under different conditions of temperature and pH. J. Appl. Bacteriol., 76, 42 18. 

Present in very small amounts but essential for metabolism of sugars and blood control. Found in yeast, wines and beer and balanced diets... 

Lactic acid is a sour principle of yogurt and lactobacillus beverages. It exhibits a soft and thick sour taste quality with slight astringency. It is a syrupy liquid produced by fermentation with a lactobacillus and is formed in the body by the metabolism of sugars. Due to its pH-controlling effect, it is used in soft drinks, pickles, Japanese sakes, sherbets, and so on. It is industrially produced by the fermentation of glucose and chemical synthesis. Approximately 12 000 tons are consumed annually as a food additive in Japan. 

Aldehydes, especially the longer chain saturated and branched chain aldehydes (i.e., propanal, butanal, 2-methyl-1-propanal, 2-methyl-1-butanal, and 3-methyl-1-butanal) are also intermediates in the formation of fusel oils. These pathways involve anabolic metabolism of sugars or transamination of amino acids. During ethanol fermentation, the aldehydes may be reduced to the corresponding alcohols by ADH enzymes and excreted into the media. Herraiz et al. (19) found that longer chain aldehydes were not as readily reduced and excreted by the yeast, e.g., 35% reduction was observed for pentanal compared to 3% reduction for decanal. 

Larger condensed phosphoric acids also occur, such as triphosphoric add, HgPgOjo. The interconversion of triphosphates, pyrophosphates, and phosphates is important in many bodily processes, including the absorption and metabolism of sugar. These reactions occur at body temperature under the influence of special enzymes (Chap. 30). 

It is a white solid used in removal of certain kinds of stains, in removing calcium ions from solutions, and in tanning leather. It occurs naturally and is toxic. The potassium and calcium salts of oxalic acid are found naturally in cabbage, spinach, and rhubarb leaves, and are also found in the bark of some species of eucalyptus trees. The metabolism of sugar by many species of mold results in the production of oxalic acid. Ingestion of large amounts can cause kidney damage, convulsions, and death. 

Glycolysis, also called as Embden-Meyerhof-Pamas pathway (EMP pathway). Glycolysis is of central importance to the metabolism of eukaryotic cells. It links the metabolism of sugars to that of organic acids in the Krebs cycle, and in anaerobic organisms, provides the principle route of energy (ATP) generation. The reactions are rather complex, but can be seen as four basic processes (Fig. 9.2) ... 

Propazine and its primary metabolite, diamino-chlorotriazine, can attenuate the pituitary LH surge, leading to disruption of estrous cycle and certain reproductive and developmental processes. Propazine causes fatty degeneration. It also blocks metabolism of sugars and carbohydrates. It may also disturb the metabolism of some of the B vitamins (thiamine and riboflavin). 

Firme, M.P., Leitao, M.C., and San Ramao, M.V. 1994. The metabolism of sugar and malic acid by Leuconostoc oenos Effect of malic acid, pH, and aeration conditions. J. Appl. Bacterial. 76, 173-181. 

Though numerous investigations show that TCA affects several biochemical processes of the plants—metabolism of sugars, lipids, nitrogen and enzyme reactions—this does not occur to an extent sufficient to explain the mode of action of a molecular level. As the protein-precipitating action of halogenated-alkanoic acids, hence of trichloroacetic acid, is well known, it is possible that the main biochemical action of TCA is the structural modification of proteins (Ashton and Crafts, 1973). 

The many phosphorylated intermediates in the metabolism of sugars will be discussed in Chapter 21. 

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