Sugar transporters acetylation

Succinyl-CoA derived from propionyl-CoA can enter the TCA cycle. Oxidation of succinate to oxaloacetate provides a substrate for glucose synthesis. Thus, although the acetate units produced in /3-oxidation cannot be utilized in glu-coneogenesis by animals, the occasional propionate produced from oxidation of odd-carbon fatty acids can be used for sugar synthesis. Alternatively, succinate introduced to the TCA cycle from odd-carbon fatty acid oxidation may be oxidized to COg. However, all of the 4-carbon intermediates in the TCA cycle are regenerated in the cycle and thus should be viewed as catalytic species. Net consumption of succinyl-CoA thus does not occur directly in the TCA cycle. Rather, the succinyl-CoA generated from /3-oxidation of odd-carbon fatty acids must be converted to pyruvate and then to acetyl-CoA (which is completely oxidized in the TCA cycle). To follow this latter route, succinyl-CoA entering the TCA cycle must be first converted to malate in the usual way, and then transported from the mitochondrial matrix to the cytosol, where it is oxida-... 

Sugar The hydrolysis of sucrose in the intestine produces both glucose and fructose, which are transported across the epithelial cells by specific carrier proteins. The fructose is taken up solely by the liver. Fructose is metabolised in the liver to the triose phosphates, dihydroxy-acetone and glycer-aldehyde phosphates. These can be converted either to glucose or to acetyl-CoA for lipid synthesis. In addition, they can be converted to glycerol 3-phosphate which is required for, and stimulates, esterification of fatty acids. The resulting triacylglycerol is incorporated into the VLDL which is then secreted. In this way, fructose increases the blood level of VLDL (Chapter 11). 

The reaction of acetyl-P with acetate kinase to form a phosphoenzyme either is an adventitious side reaction of the catalytic process or reflects some other function of acetate kinase in the E. coli cell. The latter is almost certainly correct. Acetate kinase is now known to interact with the sugar phosphate transport system (PTS) of E. coli and Salmonella typhimurium (65). This system transports sugars across the plasma membrane in the process it phosphorylates the... 

Polypeptide chains are synthesized in the cytoplasm of a cell by the process known as translation. The polypeptide may be ready for use immediately after translation or it may require further maturation steps, such as facilitated folding, complex formation, transport to another cell compartment, or covalent modification of chemical groups on the protein. The term posttranslational modifications is used for the last of these processes. Some of the modifications take place in the cytoplasm or nucleus, particularly phosphorylation and acetylation, and others take place in the endoplasmic reticulum or Golgi apparatus, particularly the addition of sugar or polysaccharide residues. 

Each plant cell manufactures its own fatty acids, since there is no lipid transport in plants. The synthesis begins with acetate which is formed from pyruvate, formed from phosphoglycerate in the Calvin cycle in leaf tissue or via degradation of sugars in seeds or fruits. De novo synthesis of fatty acids takes place in the chloroplasts of vegetative tissues or in plastids of other plant tissues. Acetate is first esterified to the -SH function of coenzyme A (CoA) via an enzyme, acetyl CoA synthetase. Coenzyme A is an adenosine derivative attached to a 4 -phosphopantetheine moiety, a chemical subunit idilch is ubiquitous in the metabolism of fatty acids. 

Metabolism For uptake and transport of G., see Lit. d-G. plays a central part in the carbohydrate metabolism. It is degraded to smaller molecules in complicated reaction sequences (glycolysis) with release of energy - one example is pyruvic acid, which can enter the citric acid cycle via acetyl-CoA - or (pentose phosphate pathway) can be converted to derivatives of other sugars for biosynthetic purposes under the concomitant availability of reduction equivalents. Alternatively d-G. can be stored in the liver and muscles as areserve substance glycogen (in plants starch). An antimetabolite of d-G. is 5-thio-D-glucose. For detection, see Lit.. ... 

It should be noted that isoprenoid biosynthesis requires acetyl-CoA, ATP, and NADPH. The physiological source of these compounds is presumably sugar phosphate metabolism, via glycolysis and the pentose phosphate pathway. We show sucrose as the starting material in Fig. 1, since it is the principal transport sugar in plants. Free acetate is not an important metabolite in plants acetyl-CoA is normally derived from pyruvate formed in glycolysis. Biosynthesis of terpenes implies that acetyl-CoA is diverted from the Krebs cycle and that the energy available from the Krebs cycle and oxidative phos-... 

Coenzyme A is the active component of transacylases transporting the residues of carboxylic acids. The most common substance is acetyl-CoA, which carries acet)4 groups. In acetyl CoA, acetic acid is bound as a thioester to the thiol group of cysteamine. Other acyl coenzymes A include malonyl-CoA, succinyl-CoA, and other coenzymes that play a role in the metabolism of proteins, fats and sugars. ACP plays a fundamental role in biosynthesis of fatty acids and polyketides. 

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