Metabohsm of carbohydrates

The modes of action for niclosamide are interference with respiration and blockade of glucose uptake. It uncouples oxidative phosphorylation in both mammalian and taenioid mitochondria (22,23), inhibiting the anaerobic incorporation of inorganic phosphate into adenosine triphosphate (ATP). Tapeworms are very sensitive to niclosamide because they depend on the anaerobic metaboHsm of carbohydrates as their major source of energy. Niclosamide has selective toxicity for the parasites as compared with the host because Httle niclosamide is absorbed from the gastrointestinal tract. Adverse effects are uncommon, except for occasional gastrointestinal upset. 

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-... 

Biotin forms part of several enzyme systems and is necessary for normal growth and body function. Biotin functions as a cofactor for enzymes involved in carbon dioxide fixation and transfer. These reactions are important in the metaboHsm of carbohydrates, fats, and proteins, as well as promotion of the synthesis and formation of nicotinic acid, fatty acids, glycogen, and amino acids (5—7). Biotin is absorbed unchanged in the upper part of the small intestine and distributed to all tissues. Highest concentrations are found in the Hver and kidneys. Little information is available on the transport and storage of biotin in humans or animals. A biotin level in urine of approximately 160 nmol/24 h or 70 nmol/L, and a circulating level in blood, plasma, or serum of approximately 1500 pmol/L seems to indicate an adequate supply of biotin for humans. However, reported levels for biotin in the blood and urine vary widely and are not a reHable indicator of nutritional status. 

Corticosteroids exhibit a wide range of physiological effects. One important function is to assist in maintaining the proper electrolyte balance in body fluids. They also play a vital regulatory role in the metabohsm of carbohydrates and in mediating the allergic response. 

Tautomerism is important in the chemistry and metabohsm of carbohydrates (Chapter 26). For example, glyceraldehyde 3-phosphate and dihydroxyacetone phosphate are two intermediates in glycolysis, a metabohc pathway in almost all organisms. 

Metabolic Functions. The formation of phosphate esters is the essential initial process in carbohydrate metaboHsm (see Carbohydrates). The glycolytic, ie, anaerobic or Embden-Meyerhof pathway comprises a series of nine such esters. The phosphogluconate pathway, starting with glucose, comprises a succession of 12 phosphate esters. 

Polylactic Acid. Polylactic acid (PLA) was introduced in 1966 for degradable surgical implants. Hydrolysis yields lactic acid, a normal intermediate of carbohydrate metaboHsm (23). PolyglycoHc acid sutures have a predictable degradation rate which coincides with the healing sequence of natural tissues. 

Oxidation to Sugar Acids and Lactones. When the aldehyde group of an aldose is oxidized, the resulting compound is an aldonic acid (salt form = aldonate) (11)4. Some aldonic acids are products of carbohydrate metaboHsm. 

The central role of the mitochondrion is immediately apparent, since it acts as the focus of carbohydrate, hpid, and amino acid metabohsm. It contains the enzymes of the citric acid cycle, P-oxidation of fatty acids, and ketogenesis, as well as the respiratory chain and ATP synthase. 

Hartmann T, Ober D (2000) Biosynthesis and Metabohsm of Pyrrolizidine Alkaloids in Plants and Specialized Insect Herbivores. 209 207-243 Haseley SR, Kamerling JP, Vliegenthart JFG (2002) UnraveUing Carbohydrate Interactions with Biosensors Using Surface Plasmon Resonance (SPR) Detection. 218 93-114 Hassner A,see Namboothiri INN (2001) 216 1-49 Helm L, see Toth E (2002) 221 61-101... 

Phaeocystis produces at least five different pools of carbohydrates, each with their own characteristics. Since the overflow metabohsm during the stationary phase of a bloom can be channeled towards glucan and mucopolysaccharides, these two pools are quantitatively the most important when the impact on the ecosystem is considered. The contribution of the pools is strongly dependent on environmental conditions. High light... 

The individual pathways of carbohydrate metabohsm in plants overlap extensively they share pools of common intermediates, including hexose phosphates, pentose phosphates, and triose phosphates. Transporters in the membranes of chloroplasts, mitochondria, amyloplasts, and peroxisomes mediate the movement of sugar phosphates between organeUes. The direction of metabolite flow through the pools changes from day to night. 

Table 18.1 summarizes important mechanisms of metahohc control. Even though we discuss them here in the context of carbohydrate metabohsm, they apply to aU aspects of metabohsm. Of the four kinds of control mechanisms listed in Table 18.1— allosteric control, covalent modihcation, substrate cychng, and genetic control—we have seen examples of allosteric control and covalent modihcation and, in Chapter 11, discussed generic control using the... 

Goenzymes are introduced in this chapter and are discussed in later chapters in the context of the reactions in which they play a role. Chapter 16 discusses carbohydrates. Chapter 17 begins the overview of the metabohc pathways by discussing glycolysis. Glycogen metabolism, gluconeogenesis, and the pentose phosphate pathway (Chapter 18) provide bases for treating control mechanisms in carbohydrate metabolism. Discussion of the citric acid cycle is followed by the electron transport chain and oxidative phosphorylation in Chapters 19 and 20. The catabolic and anabolic aspects of lipid metabohsm are dealt with in Chapter 21. In Chapter 22, photosynthesis rounds out the discussion of carbohydrate metabolism. Chapter... 

Galactosemia is an autosomal recessive disorder of carbohydrate metabohsm with an incidence of 1 in 40,000-60,000 five births in the United States [1]. Over 250 different mutations have been identified in... 

Torres NV. Modeling approach to control of carbohydrate metabohsm during citric acid accumulation by Aspergillus niger 2. Sensitivity analysis. Biotechnol Bioeng 1994 44 112-8. 

Gershanovich VN (1965) Investigation of synthesis, regulation and enzyme activity of carbohydrate metabohsm and biological oxidation in different cell systems. DSc thesis, Moscow State University, Moscow... 

Carbohydrates are the most widely distributed and abundant organic compounds on earth. They have a central role in the metabohsm of animals and plants. Carbohydrate biosynthesis in plants starting from carbon dioxide and water with the help of light energy, i. e., photosynthesis, is the basis for the existence of all other organisms which depend on the intake of organic substances with food. 

Free thiamine and its phosphoric acid esters occur in all foods, but only in some are they present in significant amounts (Table 5.8). In general, higher concentrations of thiamine (1-lOmg/kg) are found in foods that are rich in carbohydrates, which undergo intensive metaboHsm of sugars (cereals and legumes, as well as in pork meat and Hver). 

Focks, N. and Benning, C. 1998. wrinkledl A novel, low-seed-oU mutant of Arabidopsis with a deficiency in the seed-specific regulation of carbohydrate metabohsm. Plant Physiol. 118 91-101. 

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