Nucleotide-sugar substrates

FIGURE 9.1 Nucleotide sugar substrates for GTases. CMP, cytidine monophosphate GDP, guanidine diphosphate UDP, uridine diphosphate. 

Although the limitations of the enzymic reactions lie in the substrate selectivity and in the availability of enzymes and appropriate nucleotide sugar derivatives, further developments in this field will offer an interesting and efficient potential for the synthetic construction of glycopeptides of biological interest. 

This enzyme [EC 2.7.1.11], also known as phosphohexo-kinase and phosphofructokinase 1, catalyzes the reaction of ATP with D-fructose 6-phosphate to produce ADP and D-fructose 1,6-bisphosphate. Both D-tagatose 6-phosphate and sedoheptulose 7-phosphate can act as the sugar substrate. UTP, CTP, GTP, and ITP all can act as the nucleotide substrate. This enzyme is distinct from that of 6-phosphofructo-2-kinase. See also ATP GTP Depletion... 

Glucose and 0-toluoylglucosamine bind to these crystals in the deep cleft that separates the lobes of each subunit (70). ADP or AMP-PNP only bind in the presence of a sugar substrate or inhibitor. Only one nucleotide binds per dimer, and its binding site is located at the point of contact between the two subunits (72). Parts of the binding site are on each subunit. This site has been labeled the I site (72). A schematic drawing of the BII structure with the location of the various binding sites is shown in Fig. 16 (72). 

The now-classical solution to these problems is to attach the enzyme to a suitable polymer which is used as an aqueous suspension. When the reaction is finished, the enzyme is separated from the products by filtration, and, not infrequently, may be used again many times. In the operation of the D-galac-tosylation cycle described in Section V,2, only catalytic quantities of nucleotide-sugars are necessary, as they are constantly regenerated in the medium by the interplay of appropriate substrates with other enzymes, also present in the immobilized state. 

On the other hand, the enzymatic synthesis of glycoconjugates and oligosaccharides leads to high product yields in a short time by stereo- and regioselective one-step reactions. All enzymatic reactions are easy to scale up and are carried out in aqueous media under mild conditions. A whole set of enzymes is now available to build up OAT bonds in monosaccharides, COP bonds in activated monosaccharides e.g. phosphorylated sugars or nucleotide sugars, and C-O-C bonds in di- and oligosaccharides (Fig. 1). However, all these enzymatic reactions are limited by the substrate spectrum of the individual enzyme. 

Fig. 17. Nucleotidyltransferase substrate screening assay (NUSSA). A Nucleotide sugar-synthesizing nucleotidyltransferase (EC 2.7.7), B PPrdependent phosphofructokinase (EC 2.7.2.90), C Aldolase (EC 4.1.2.13), D Triose-phosphate isomerase (EC 5.3.1.1), E Glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) [336]...

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