Glucan reaction

Starch is stored in plant cells in the form of granules in the stroma of plas-tids (plant cell organelles) of two types chloroplasts, in which photosynthesis takes place, and amyloplasts, plastids that are specialized starch accumulation bodies. When starch is to be mobilized and used by the plant that stored it, it must be broken down into its component monosaccharides. Starch is split into its monosaccharide elements by stepwise phosphorolytic cleavage of glucose units, a reaction catalyzed by starch phosphorylase (Figure 7.23). This is formally an a(1 4)-glucan phosphorylase reaction, and at each step, the prod-... 

Chitosan, having a similar chemical backbone as cellulose, is a linear polymer composed of a partially deacety-lated material of chitin [(l-4)-2-acetamide-2-deoxy-/3-D-glucan]. Grafting copolymer chains onto chitosan can improve some properties of the resulting copolymers [48-50]. Yang et al. [16] reported the grafting reaction of chitosan using the Ce(IV) ion as an initiator, but no detailed mechanism of this initiation has been published so far. 

Kobayashi, M., and Ichishima, E. (1991) Application of periodate oxidized glucans to biochemical reactions./. Carbobydro Chem. 10, 635-644. 

If branching is (1 —> 3), no glycol grouping will be present in any central unit and it may be seen that reaction will only occur on the terminal units. Such is the case with the polysaccharide laminarin, with the glucan of yeast membrane, and with a galactose-containing polysaccharide isolated from agar.146-148... 

Kobayashi S, Koga K, Hayashida O, Nakano Y and Hasegawa Y (1990) Specific inhibition of insoluble glucan synthase (GTF-1) by Maillard reaction products from casein and albumins. Agric Biol Chem 54, 1417-1424. 

Cellobiohydrolase I (CBH I, 1,4-jS-D-glucan-cellobiohydrolase, E.C. 3.2.1.91) is the main protein (ca. 60%) of the cellulase complex produced by T. reesei strains. CBH I hydrolyses crystalline cellulose, acid swollen cellulose and 4-methylumbelliferyl-cellodex-trins by cleaving off the terminal cellobiose unit from the non reducing end of the chain. It operates with retention of configuration in the reaction products 19,20. The abundance of this enzyme and its stability has facihtated its purification to homogeneity... 

In this paper, it has been shown that glucansucrases with different synthetic specificities can synthesize glucans with different structures and can synthesize oligosaccharides with different structures by acceptor reactions. The mechanisms by which these enzymes carry out the polymerization and by which the acceptor reactions occur has been discussed. The products resulting from the... 

This enzyme [EC 2.4.1.4], also referred to as sucrose-glucan glucosyltransferase, catalyzes the reaction of sucrose with a glucan (specifically, [(l,4)-o -D-glucosyl] ) to yield D-fructose and a longer glucan (that is, [(l,4)-o -D-glucosyl] +i). 

Heller and Villemez299,300 solubilized, but did not separate, the D-mannosyltransferase and D-glucosyltransferase activities from this particulate-enzyme system, and found that, when only GDP-D-mannose is provided as the substrate, a/ -(1— 4)-linked D-mannan is synthesized and, when only GDP-D-glucose is present, ap-(l— 4)-linked D-glucan is produced. They further noted, with this transferase system, that incorporation of D-glucose from GDP-D-glucose into polysaccharide is a shortlived reaction that can be greatly extended if GDP-D-mannose is also included in the reaction mixture. 

On the basis of the data, it was concluded1 that the synthetic polyglucoses obtained by this method are linear, /3-d- (1— 4) -linked glucans which possess properties similar to those of cellulose. It is especially significant that this polymerization proceeded with apparent stereospecificity, to form only the /S-d anomeric linkage. The mild conditions under which the polycondensation occurs probably contribute to this selectivity of reaction. 

Enzymic hydrolysis of a jS-D-glucan fraction from the cell wall of Piricularia oryzae454,455 released 3-O-gentiobiosyl-D-glucose (118) and gen-tiotriose, indicating possible differences in structure from that of the polymer separated from Sclerotium sp. On reaction of the alkali-insoluble glucan... 

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