UDP-glucose- pyrophosphorylase

Recently, we have purified the potato tuber enzyme,56) modified the enzyme with several types of PLP analogues,17,54) cloned its cDNA,37) and constructed the expression system in E. coli.sg) Fig. 4.2 shows the structures of the reagents used for the modification of the enzyme in comparison with that of the substrate. Although UP2-PL and UP3-PL bound to the enzyme in a 1 1 stoichiometry, five lysyl residues (Lys-263, Lys-329, Lys-367, Lys-409, and Lys-410) were labeled in varying degrees (Table 4.2). Pyridoxal-diphos- 

Reagent Residual activity (%) Relative amounts of label (%)  

The results of site-directed mutagenesis studies are generally consistent with this model.583 Table 4.3 summarizes the kinetic parameters of the mutant enzymes where the five labeled lysyl residues are individually replaced by Gin. The Lys-367/Gin enzyme was almost completely inactive. The Lys-263/ Gin enzyme had slight activity with decrease in affinity to pyrophosphate and glucose 1-phosphate. The Lys-329/Gin enzyme also had considerably lower affinity to the two substrates, but possessed a Kraax value comparable to the wild-type enzyme. The replacements of Lys-409 and Lys-410 by Gin did not change the kinetic properties of the enzyme. The kinetic properties of the Lys-329/Gin enzyme suggest that Lys-329 interacts with pyrophosphate after UDP-glucose binds to the active site. 

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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 ... 

FIGURE 23.18 The UDP-glucose pyrophosphorylase reaction is a phosphoanhydride exchange, with a phosphoryl oxygen of glu-cose-l-P attacking the m-phosphorus of UTP to form UDP-glucose and pyrophosphate. 

There is some difficulty in correlating results of PAN exposure in vfvo with the above types of in vitro studies. For example, UDP glucose pyrophosphorylase is very susceptible to PAN in vitro, but in vivo there is a stimulation of enzymatic activity (at 112 ppm for 6 min). It is also... 

Hall, M. A., and L. Ordin. Subcellular location of phosphoglucomutase and UDP glucose pyrophosphorylase in avena coleoptiles. Physiol. Plant. 20 624-633, I%7. 

In fluorine-18 chemistry some enzymatic transformations of compounds already labelled with fluorine-18 have been reported the synthesis of 6-[ F] fluoro-L-DOPA from 4-[ F]catechol by jS-tyrosinase [241], the separation of racemic mixtures of p F]fluoroaromatic amino acids by L-amino acylase [242] and the preparation of the coenzyme uridine diphospho-2-deoxy-2-p F]fluoro-a-o-glucose from [ F]FDG-1-phosphate by UDP-glucose pyrophosphorylase [243]. In living nature compounds exhibiting a carbon-fluorine bond are very rare. 

Sowokinos, J. R. (2001a). Pyrophosphorylase in Solanum tuberosum L. Allelic and isozyme patterns of UDP-glucose pyrophosphorylase as a marker for cold-sweetening resistance in potatoes. American Journal of Potato Research, 78, 57-64. 

For many biosynthetic reactions that liberate pyrophosphatase activity makes the process more favorable energetically, tending to make these reactions irreversible. In plants, this enzyme is present in plastids but absent from the cytosol. As a result, the cytosol of leaf cells contains a substantial concentration of PP,— enough ( 0.3 him) to make reactions such as that catalyzed by UDP-glucose pyrophosphorylase (Fig. 15-7) readily reversible. Recall from Chapter 14 (p. 527) that the cytosolic isozyme of phosphofructokinase in plants uses PPi, not ATP, as the phosphoryl donor. 

UDP-glucose pyrophosphorylase catalyzes the synthesis of UDP-glucose (see Fig. 1) from UTP and glucose 1-phosphate ... 

Fig. 4.3 A hypothetical model for the location of five lysyl residues around the substrates bound to potato tuber UDP-glucose pyrophosphorylase, constructed based on the results of the comparative affinity labeling.541 (Reproduced with permission from J. Biochem., 110, 713 (1991)).

Vilches, S., Canals, R., Wilhelms, M., Salo, M.T., Knirel, Y.A., Vinogradov, E., Merino, S., Tomas, J.M. Mesophilic Aeromonas UDP-glucose pyrophosphorylase (GalU) mutants show two types of lipopolysaccharide structures and reduced virulence. Microbiology 153 (2007) 2393-2404. 

Fig. 6.—Hypothetical Model for the Biosynthesis of Cellulose.184 [Numbers refer to reactions catalyzed by the following enzymes 1, invertase (EC 3.2.1.26) 2, sucrose synthetase 3, hexokinase (EC 2.7.1.1) 4, phosphoglucomutase (EC 2.7.5.1) 5, UDP-glucose pyrophosphorylase and 6, 7, and 8, hypothetical reactions in the pathway to cellulose.]...

The glucose 1-phosphate is then activated to enable its incorporation into glycogen. This activation involves the expenditure of energy derived from the hydrolysis of a molecule of uridine triphosphate (UTP) by UDP-glucose pyrophosphorylase. 

The first chiral phosphates to be used for stereochemical analyses were chiral phosphorothioates, which were used to determine the stereochemical courses of ribonuclease, UDP-glucose pyrophosphorylase, adenylate kinase and several other kinases and synthetases. The chiral phosphorothioates either had sulfur in place of an oxygen at an otherwise prochiral center of a phosphodiester or phosphoanhydride or stereospecifically placed sulfur and 180 (or nO) in a terminal phosphoryl group. The syntheses and configurational analyses of the most important of these compounds are outlined in the following. 

The diastereomers of UTPaS and UDPaS-glucose can be separated by the action of yeast UDP-glucose pyrophosphorylase according to Equations 5 and 6 [21] ... 

Fig. 29. Stereochemical course of uridylyl transfer by UDP-glucose pyrophosphorylase.

Two pairs of chemically matched reactions exemplify the importance of shared binding sites in the evolution of double-displacement pathways. They are the reactions catalyzed by UDP-glucose pyrophosphorylase (inversion) [74] and galactose- -P uridylyltransferase (retention) [21], which catalyze Reactions 21 and 22,... 

Ozbun, J. L., Hawker, J. S., Greenberg, E., Lammel, C, Preiss, J., and Lee, E. Y. C. 1973. Starch synthetase, phosporylase, ADPglucose pyrophosphorylase and UDP-glucose pyrophosphorylase in developing maize kernels. Plant PhysioL 51,1-5. 

Sowokinos, J. R. 1976. Pyrophosphorylase in Solarium tuberosum. I. Changes in ADP-glucose and UDP-glucose pyrophosphorylase. Plant Physiol. 57, 63-68. 

In yeasts, the catalytic amounts of uridine 5-(D-glucosyl dihydrogen pyrophosphate) necessary could also be formed by the action of UDP-glucose pyrophosphorylase, which catalyzes the reaction ... 

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. 

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