A-Glucosyl transferases

Production of palatinose from sucrose under the action of the intracellular a-glucosyl-transferase in Protaminobacter rubrum (Mitsui Seito Co., Ltd.). Palatinose is a useful substitute for sucrose with low insulin stimulation annual production 4000 tons. 

Experimentally, the major gap in our knowledge concerns attack on, and departure from, glycosyl centres by nitrogen. There is additionally always the possibility that more careful analysis of the products of enzyme reactions may turn up unusual reactions - such as the production of 1,6-anhydropyranose units by a glucosyl transferase [180] or phage A lysozyme [181]. 

Scheme 1. General mechanism of a-glucosyl transferases. R may be one of a variety of aglycones. R OH may represent water or the non-reducing terminus of an oligosaccharide.

Loutre, C. et al. (2003) Isolation of a glucosyl-transferase from Arabidopsis thaliana active in the metabolism of the persistent pollutant 3, 4-dichloroaniline. Plant J. 34, 485 93... 

FIGURE 6.20 A disaccharide of galactose and glucose is covalently linked to the 5-hydroxyl group of hydroxylysines in collagen by the combined action of the enzymes galactosyl transferase and glucosyl transferase. 

E. A. MacGregor, H. M. Jespersen, and B. Svensson, A circularly permuted alpha-amylase-type alpha/beta-barrel structure in glucan-synthesizing glucosyl-transferases, FEBS Lett., 378 (1996) 263-266. 

Monosaccharide attachment to some of the hydroxylysine residues within the a chains occurs at this stage as galactose (gal) and glucose (glc) residues are added by specific galactosyl transferase and glucosyl transferases. The carbohydrates are attached as single monosaccharides or as gal-glc disaccharides. 

Nagatoshi M, Terasaka K, Nagatsu A, Mizukami H. An Iridoid-Specific Glucosyl-transferase from Gardenia jasminoides. JBC July, 2011 1-19. Available from http // www.jbc.org/cgi/doi/10.1074/jbc.Mlll.242586 (accessed 20 September 2012). 

Figure 3-14. Possible biosynthetic route towards coumarin. (a) 2-hydroxylase, (b) glucosyl transferase, (c) P-glucosidase, (d) dimethylallyl transferase and/or UV light. The enzymes have not yet been identified.

The pathogenesis of dental caries may involve three distinct processes (1) adherence of the bacteria to the tooth, (2) formation of glycocalyx due to synthesis of a sticky glucan by the action of the bacterial enzyme glucosyl transferase on sucrose, and (3) accumulation of biobUm (plaque), within which there is continuing acid production by constituent bacteria (including streptococci and lactobacflli) able to metabolize carbohydrates at low pH values. This acid demineralizes an enamel. 

Fig. 1. Simplified diagram of the phenylpropanoid and flavonoid biosynthetic pathways. Enzymes that catalyze the reactions are placed on the left-hand side, and transcription factors on the right-hand side of the arrows. Both transcription factors for which their control over the enzymatic steps has been genetically proven, as well as transcription factors that have been shown to interact with promoters of the structural genes, are shown. PAL Phenylalanine ammonia lyase C4H cinnamate 4-hydroxylase 4CL 4-coumaroyl-coenzyme A ligase CHS chalcone synthase CHI chalcone-flavanone isomerase F3H flavanone 3(3-hydroxylase DFR dihydroflavonol 4-reductase AS anthocyanin synthase UFGT UDP glucose-flavonol glucosyl transferase RT anthocyanin rhamnosyl transferase...

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