Enzymes, carbohydrate synthesis

A more general access to biologically important and structurally more diverse aldose isomers makes use of ketol isomerases for the enzymatic interconversion of ketoses to aldoses. For a full realization of the concept of enzymatic stereodivergent carbohydrate synthesis, the stereochemically complementary i-rhamnose (Rhal EC 5.3.1.14) and i-fucose isomerases (Fuel EC 5.3.1.3) from E. coli have been shown to display a relaxed substrate tolerance [16,99,113,131]. Both enzymes convert sugars and their derivatives that have a common (3 J )-OH configuration, but may deviate in... 

Hager M, Currie F, Holmberg K (2003) Organic Reactions in Microemulsions. 227 53-74 Hausler H, Stiitz AE (2001) d-Xylose (d-Glucose) Isomerase and Related Enzymes in Carbohydrate Synthesis. 215 77-114... 

Mutations resulting in ethambutol resistance can arise spontaneously. The exact changes are unknown but may involve enzymes in carbohydrate synthesis pathways. 

Carbohydrate metabolism in the organism tissues encompasses enzymic processes leading either to the breakdown of carbohydrates (catabolic pathways), or to the synthesis thereof (anabolic pathways). Carbohydrate breakdown leads to energy release or intermediary products that are necessary for other biochemical processes. The carbohydrate synthesis serves for replenishment of polysaccharide reserve or for renewal of structural carbohydrates. The effectiveness of various routes of carbohydrate metabolism in tissues and organs is defined by the availability of appropriate enzymes in them. 

The fhioethyl group present in the anchor group of (40) was activated by treatment with N-iodosuccinimide (NIS) followed by displacement with a variety of alcohols (44-46). To prove the possible application of this linker in solid phase carbohydrate synthesis, protected glycosides (47) and (48) were coupled to linker (40) and released enzymatically. Flitsch et al. also described the immobilization and enzymatic cleavage on a variety of amines [41]. Nevertheless, the application of this enzyme-labile hnker group in multi-step syntheses on the solid phase and subsequent enzyme-initiated release from the polymeric support has not been described yet. 

Toone, E., Simon, E., Bednarski, M. and Whitesides, G. (1989) Enzyme-catalyzed synthesis of carbohydrates. Tetrahedron, 45, 5365-5422. 

In plants, certain invertebrates, and some microorganisms (including E. coli and yeast) acetate can serve both as an energy-rich fuel and as a source of phosphoenolpyruvate for carbohydrate synthesis. In these organisms, enzymes of the glyoxylate cycle catalyze the net conversion of acetate to succinate or other four-carbon intermediates of the citric acid cycle ... 

M.-J. Kim, W. J. Hennen, H. M. Sweers, and C.-H. Wong, Enzymes in carbohydrate synthesis 79-Acetylneuraminic acid aldolase catalyzed reactions and preparation of 7V-aceiyl-2-deoxy-D-neuraminic acid derivatives, J. Am. Chem. Soc. 770 6481 (1988). 

A reversible covalent modification that plants use extensively is the reduction of cystine disulfide bridges to sulf-hydryls. Many of the enzymes of photosynthetic carbohydrate synthesis are activated in this way (table 9.3). Some of the enzymes of carbohydrate breakdown are inactivated by the same mechanism. The reductant is a small protein called thioredoxin, which undergoes a complementary oxidation of cysteine residues to cystine (fig. 9.5). Thioredoxin itself is reduced by electron-transfer reactions driven by sunlight, which serves as a signal to switch carbohydrate metabolism from carbohydrate breakdown to synthesis. In one of the regulated enzymes, phosphoribulokinase, one of the freed cysteines probably forms part of the catalytic active site. In nicotinamide-adenine dinucleotide phosphate (NADP)-malate dehydrogenase and fructose-1,6-bis-... 

Wong C-H, Drueckhammer DG, Durrwachter JR, Lacher B, Chauvet CJ, Wang YF, Sweers HM, Smith GL, Yang LJS, Hennen WJ (1989) Enzyme-catalyzed synthesis of carbohydrates. In Horton D, Hawkins LD, McGarvcy GJ (eds) Trends in Synthetic Carbohydrate Chemistry. American Chemical Society, Washington, vol. 386, p 317... 

Mazur AW (1991) Galactose Oxidase Selected Properties and Synthetic Applications. In Bednarski MD, Simon ES (eds) Enzymes in Carbohydrate Synthesis. American Chemical Society, Washington, vol. 466, p 99... 

Chemoenzymatic approach served as an alternative method for the synthesis of complex carbohydrate-containing molecules. The use of biosynthetic enzymes not only provides high regioselectivity and stereoselectivity for the formation of glycosidic bonds but also solves the problems of protection and deprotection steps required by chemical synthesis. The discovery of bacterial counterparts and the advance in bioengineering technology led to breakthroughs in complex carbohydrate synthesis. 

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