Pyrophosphorylases sugar nucleotide

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 reaction is catalyzed by specific enzymes, usually termed204 sugar nucleotide pyrophosphorylases. The equilibrium constant is not far from unity, and addition of inorganic pyrophosphatase, an enzyme that converts inorganic pyrophosphate irreversibly into... 

The lack of absolute substrate specificity with the sugar nucleotide pyrophosphorylases allows the preparation of some analogs of the natural derivatives. The yeast pyrophosphorylase effective for synthesis of uridine 5 -(a-D-glucopyranosyl pyrophosphate) was used for synthesis of the analogous derivatives of pseudouridine228 (48) and 5-hydroxyuridine229 (49). 

UDP-GlcNAc UDP-GlcNAc Pyrophosphorylase yeast, Nucleotide sugar [279]... 

The sugar nucleotides UDPglucose and ADPglucose can be synthesized in plants either by a pyrophosphorylase-type reaction (reactions 3a and 3b Espada, 1962) or via a reversal of the sucrose synthase reaction (reaction 4 Cardini et ai, 1955 de Fekete and Cardini, 1964)... 

Hopper, J.E., and Dickinson, D.B., 1972, Partial purification and sugar nucleotide inhibition of UDP-glucose pyrophosphorylase from Lilium longiflorum pollen. Arch. Biochem. Biophys. 148 523-535. 

Enzymatic giycosyiation using sugar nucieotide recyciing systems. Ei = pyruvate kinase, E2 = sugar nucleotide pyrophosphorylase, E3 = pyrophosphatase, E4 = sugar nucleotide synthase, E5 = myokinase, PEP = phosphoenol pyruvate, Pyr = pyruvate... 

From this brief survey, it is seen that there were few features of carbohydrate metabolism in plants that escaped Hassid s touch, and much that we now know about the role of sugar nucleotides in the interconversion of carbohydrates in plants is a direct result of his persistent effort. From the incorporation of labelled precursors into monosaccharides, to the conversion of the monosaccharides into their glycosyl phosphates, to the action of the pyrophosphorylases in the synthesis of glycosyl esters of nucleoside pyrophosphates, to the interconversion of the resulting sugar nucleotides, to the polymerization of the activated monosaccharides to yield disaccharides and the homopolysaccharides, and, finally, to the modification of the polysaccharides by methylation—in summary, to almost every aspect... 

Thus, in the first group of bacteria, GDP-D-mannose inhibits its own synthesis by a simple feed-back inhibition. A similar mechanism is also operative in the second group, where GDP-L-fucose inhibits both GDP-D-mannose pyrophosphorylase and GDP-D-mannose oxi-doreductase. In the third group, where both sugar nucleotides are needed for polysaccharide synthesis, their biosynthesis is individually controlled, so that imbalance in the supply of these two sugars will not occur. 

This G-l-P must now be combined to form another sugar nucleotide, ADPG, by ADPG pyrophosphorylase ... 

In a system where UDP-Gal regeneration is the goal, the inclusion of a one-step conversion of UTP to UDP-Gal using the enzyme UDP-Gal pyrophosphorylase would be ideal. Unfortunately, this enzyme is not commercially available, nor is it easy to prepare from biological sources [8]. Luckily, an alternative biosynthetic pathway to UDP-Gal exists. In nature, UDP-Glc is a central intermediate for the biosynthesis of UDP-Gal and UDP-GlcUA, as well as other sugar nucleotides. The enzyme UDP-Glc pyrophosphorylase (UDPGP EC 2.1.1.9) required for the conversion of UTP to UDP-Glc can be purchased. The UDP-Gal 4-epimerase... 

The same procedure was applied212 for the preparation of uridine 5 -(a-D-glucopyranosyl pyrophosphate-4"-t, or -5"-f. A cell-free extract of Phytophthora cinnamoni was used for the synthesis of the 6"-t derivative,213 as well as yeast pyrophosphorylase.2133 An enzyme from Salmonella typhimurium was found quite satisfactory214 for obtaining this and other labeled nucleotide sugars. ... 

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