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Energy metabolism oxaloacetate

Studies of the carbohydrate metabolism of T. cruzi (21) have shown that phos-phoenolpyruvate serves as the acceptor of the primary COj-fixation reaction. This resulted in the formation of oxaloacetate and malate and the excretion of succinate. The central role of PEPCK in energy metabolism in insect-stage trypanosomatids has been illustrated in the case of T. cruzi epimastigotes, using 3-mercaptopicolinic aeid, a powerful inhibitor of this enzyme (22). Inhibition led to a twofold reduction in the anaerobic production of succinate and a similar decrease in glucose consumption, while the production of alanine, via the transamination of pyruvate, increased threefold. [Pg.24]

Acetyl-CoA. There is a key metabolite of energy metabolism. It is produced in mitochondria by decarboxylation of pyruvate, beta oxidation of fatty acids, or hydrolysis of acetoacetate. In condensation reaction with oxaloacetate, acetyl-CoA yields citrate, which is the first intermediate in the tricarboxylic acid chain. Acetyl-CoA is also used for the synthesis of acetylcholine and the acetylation of several low molecular weight compounds and proteins. In liver and adipose tissue, acetyl-CoA is used for the synthesis of the fatty acids chain. [Pg.598]

Fat is only an energy storage form (Fig. 17-4). Fat cannot be converted to carbohydrate equivalents. This is a very important point. Remember it The reason for this is a bit subtle. The carbon skeleton of fatty acids is metabolized to acetyl-CoA only. Glucose precursors such as oxaloacetate can be synthesized from acetyl-CoA by going around the TCA cycle. However, acetyl-CoA has 2 carbon atoms. Going around the TCA cycle burns off 2 carbon atoms (as C02). The net number of carbon atoms that ends up in oxaloacetate is then zero. No carbohydrate can be made from fat.5... [Pg.220]

To replace losses, oxaloacetate can be synthesized from pyruvate and C02 in a reaction that uses ATP as an energy source. This is indicated by the heavy gray line leading downward to the right from pyruvate in Fig. 10-1 and at the top center of Fig. 10-6. This reaction depends upon yet another coenzyme, a bound form of the vitamin biotin. Pyruvate is formed from breakdown of carbohydrates such as glucose, and the need for oxaloacetate in the citric acid cycle makes the oxidation of fats in the human body dependent on the concurrent metabolism of carbohydrates. [Pg.515]

A small number of other biosynthetic pathways, which are used by both photosynthetic and nonphotosynthetic organisms, are indicated in Fig. 10-1. For example, pyruvate is converted readily to the amino acid t-alanine and oxaloacetate to L-aspartic acid the latter, in turn, may be utilized in the biosynthesis of pyrimidines. Other amino acids, purines, and additional compounds needed for construction of cells are formed in pathways, most of which branch from some compound shown in Fig. 10-1 or from a point on one of the pathways shown in the figure. In virtually every instance biosynthesis is dependent upon a supply of energy furnished by the cleavage to ATP. In many cases it also requires one of the hydrogen carriers in a reduced form. While Fig. 10-1 outlines in briefest form a minute fraction of the metabolic pathways known, the ones shown are of central importance. [Pg.517]

Tie reactions constitute a metabolic motif that we will see again in fatty acid synthesis and degradation as well as in the degradation of some amino acids. A methylene group (CH2) is converted into a carbonyl group (C=0) in three steps an oxidation, a hydration, and a second oxidation reaction, Oxaloacetate is thereby regenerated for another round of the cycle, and more energy is extracted in the form of FADH and NADH. [Pg.487]


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See also in sourсe #XX -- [ Pg.391 , Pg.392 , Pg.395 ]




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