Nucleotide sugar

Nucleotide sugars Nucleotide triphosphates NUCLO-ADD Nuctalon NUDAT Nude... 

Glucose Units Are Activated for Transfer by Formation of Sugar Nucleotides... 

We are familiar with several examples of chemical activation as a strategy for group transfer reactions. Acetyl-CoA is an activated form of acetate, biotin and tetrahydrofolate activate one-carbon groups for transfer, and ATP is an activated form of phosphate. Luis Leloir, a biochemist in Argentina, showed in the 1950s that glycogen synthesis depended upon sugar nucleotides, which may be... 

Sugar nucleotides are formed from sugar-l-phosphates and nucleoside triphosphates by specific pyrophosphorylase enzymes (Figure 23.18). For example, UDP-glucose pyrophosphorylase catalyzes the formation of UDP-glucose from glucose-l-phosphate and uridine 5 -triphosphate ... 

The net reaction for sugar nucleotide formation (combining the preceding two equations) is thus... 

L. F. Leloir (Buenos Aires) discovery of sugar nucleotides and their role in the biosynthesis of carbohydrates. 

Figure 7.9 Interconversion of sugar phosphates and sugar nucleotide phosphates. Adapted from "Biotechnology of microbial exopolysaccharides". IW Sutherland, Cambridge University Press, 1990.

There is a second large gene duster, about 35kb, also involved in the synthesis of xanthan. The predse function is unknown but it is thought to encode for proteins involved in the synthesis of sugar nucleotide diphosphates. 

The genes responsible for encoding the proteins specifically involved in exopolysaccharide synthesis are dustered in one large operon. The genes encoding the proteins for sugar nucleotide phosphates, which are not necessarily spedfically used for exopolysaccharide synthesis, also tend to be dustered. 

The type-specific capsular polysaccharide from Streptococcus pneumoniae type 5 contains 2-acetamido-2,6-dideoxy- -D-x>>/o-hexopyranosyl-4-ulose residues (17). Sugar nucleotides of hexos-4-uloses are important intermediates in the transformation of sugars during the biosynthesis, but this is the only known example of such a sugar as a polysaccharide component. 

Epimerization at C-5 of hexuronic acids is a reaction that proceeds both on the polymer and on the sugar nucleotide level. In addition to the three pairs of parent acids, namely, the u-glucolL-ido-, D manno/L-gulo-, and D-ga-lacto/L-altro-he uron c acids, the 2-amino-2-deoxy acids belonging to the last two and the 2,3-diamino-2,3-dideoxy acids belonging to the middle pair have been found. 

The biosynthesis of Kdo and neuraminic acid is known to involve enol-pyruvate phosphate and D-arabinose or 2-acetamido-2-deoxy-D-mannose, respectively. Nothing is known about the biosynthesis of all the other glycu-losonic acids. One interesting problem is, for example, whether the two 5,7-diamino-3,5,7,9-tetradeoxynonulosonic acids are synthesized analogously to neuraminic acid, from a three- and a six-carbon fragment, by modification of neuraminic acid on the sugar nucleotide level, or by a third, less obvious route. 

Chen, X., Fang, J., Zhang, J.etal. (2001) Sugar nucleotide regeneration beads (superbeads) a versatile tool for the practical synthesis of oligosaccharides. Journal of the American Chemical Society, 123, 2081-2082. 

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