Glycosyltransferase enzyme

Primary and secondary nucleotide sugars are needed for the preparative synthesis of glycoconjugates with glycosyltransferases. Enzymes for the formation... 

Griffiths G, Cook NJ, Gottfridson E, Lind T, Lidholt K, Roberts IS. Characterization of the glycosyltransferase enzyme from the Escherichia coh K5 capsule gene cluster and identification and characterization of the glucuronyl active site. J. Biol. Chem. 1998 273 11752-11757. 

In addition to the glycosyltransferase enzymes, the substrate specificity of the teicoplanin acyl-transferase (Atf), responsible for the installation of the fatty acid amide in teicoplanin, has been examined [168]. This enzyme appears to be tolerant to modifications in the amide chain length, carbohydrate structure and nature of the aglycone. This finding is of particular interest as it has been shown that installation of the lipid containing monosaccharide from teicoplanin onto vancomycin can restore antibiotic activity against several resistant strains [159]. 

From dihydrokaempferol, dihydroquercetin and dihydromyricetin -by action of enzyme flavonol synthetase (FLS) - kaempferol, quercetin and myricetin respectively are formed. As flavonols are present in the glycoside form, analogous to anthocyanins, it is supposed that the beginning of their synthesis is concomitant with the flavonol-3-O-glycosyltransferase enzyme formation, at the veraison beginning. 

In nature, glycosyltransferase enzymes accomplish the daunting task of the construction of diverse and complex oligosaccharide [7-9]. These enzymes catalyze... 

Glycosyltransferase enzyme structure is divided into two domains N-terminal domain A and C-terminal domain B. It has been noted that all glycosyltransferases... 

Table 2 Microbial Glycosyltransferase Enzymes for Which an Overexpression System Has Been Developed... 

The need for oligosaccharides will grow in proportion to the number of their applications. Cost-effective methods of their synthesis are clearly needed. It is also clear that much further work will he required in this field. Only three glycosyltrans-ferase crystal structures are cmrently available, and only one of these is a microbial glycosyltransferase [14]. The exact mechaiusm of action of these enzymes still awaits elucidation. However, as more and more of glycosyltransferase enzymes became available, their synthetic usefulness will inevitably increase and, as the first wholecell attempts [69,70] show, the use of microhial glycosyltransferases can he facile, efficient, and full of possibilities. 

Synthesis of other polysaccharides involves many of the same mechanisms as for glycogen, particularly the use of nucleotide-linked sugars as activated biosynthetic intermediates and glycosyltransferase enzymes. Biosynthesis of several polysaccharides is described briefly below ... 

The controversy still existing about the biosynthesis of gangliosides in various tissues has not been resolved by the study of glycosyltransferase enzymes. The... 

Fig. 8. Specificity of sialyltransfer to Galp( 1-3)GalNAc by purified sialyltransferases. Glycosyltransfer to the disaccharide using purified glycosyltransferase enzymes is shown.

In addition to its antioxidant role, ascorbic acid functions to keep various metallic ions in catalytic centers in their reduced forms. For example, some oxygenases require iron or copper in their Fe + or Cu+ states of oxidation. If these protein-bound ions are accidentally left in a more oxidized state they may need to be reduced by ascorbate ions. While this is a protectant role, there are some enzymes for which ascorbate has become a cosubstrate. An example is dopamine -hydroxylase, which converts dopamine to the neurotransmitter noradrenaline. The enzyme contains copper which cycles between Cu+ and Cu +, as it incorporates one atom of oxygen from O2 into its substrate. Ascorbate supplies the electrons for reduction of the second atom of the O2 to H2O. A recent report describes another distinct function for ascorbate ion. It apparently acts as a basic catalytic group for proton abstraction from a water molecule during the action of a glycosyltransferase enzyme, becoming part of the active site of that enzyme. 

Cyclodextrin glycosyltransferase Enzymes that cleave starch and cyclize linear dextrins into a cyclodextrin ring. 

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