Glucan derivatives, structural cellulose

Single crystals of the D-glucan from Acetobacter xijlinum were prepared in water-methanol solutions at room temperature. Using electron and X-ray diffraction, a hexagonal unit-cell, with a = h = 0.518 nm and c = 2.0 nm, was derived. It was concluded that the chain axes lie parallel to the surface of the lamellar crystals, that there are 2.5 water molecules per /3-D-Glcp residue, and that the structure is similar to that of cellulose hydrate II (Ref. 42). 

Figure 8-4. Methylation analysis of in vitro P-D-glucans. (a) Gas chromatography of the permethyl-ated alditol acetate obtained from methylation analysis of the cellulose synthesized in vitro by the enzyme from blackberry. Peak 1, derivative characteristic of (1 4) linked glucosyl units. Peak 2, internal standard (mj o-inositol). The derivative characteristic of (1 3) linked glucosyl units usually elutes 1 min before the major derivative visible in the chromatogram (not shown see Bulone et al. 1995). (b) Structural characterization by electron impact mass spectrometry of the 1,4,5-tri-0-acetyl-2,3,6-tri-0-methyl-D-glucitol derivative corresponding to peak 1 in A and characteristic of (1 4) linked glucosyl units.

We can give here an example of topolytic activity of ceUulases (which means the capability of the enzyme to run reactions on the surface of insoluble substrate without deep destmction of cellulose structure), particularly of endo-P-l,4-glucanases (EGs). These enzymes have hydrolytic activities toward polyglucans containing p-l,4-glycosidic bonds, which include cotton and wood cellulose, different soluble cellulose derivatives, p-glucans of oat and barley, and other polysaccharides. Hydrolysis of cellulose by EGs occurs by endo-depolymerization mechanism. 

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