Glucans methylation

Several methylated sugars have been identified in hydrolyzates of LPS, cell-wall polysaccharides, and extracellular polysaccharides. A considerable number of these have been found in the LPS from photosynthetic prokaryotes. Two polysaccharides from Mycobacterium species, a glucan" and a mannan" are remarkable in that they contain high percentages of methylated sugars. Glycolipids from Mycobacterium species are also rich in methylated sugars, some of which have not been found elsewhere, but this is beyond the scope of the present article. 

The synthesis of linear 4 —> 1-a-D-glucans from D-glucopyranosyl phosphate by the action of phosphorylases has been shown by comparison of results of methylation and end-group assay and viscosity determination,209 and by potentiometric, iodine titrations82 on the product. The chain length of the enzymic product (100 to 200 D-glucose units) is less than that of the natural component. Whether this is due to impure enzymes cannot yet... 

Our original approach to polysaccharide C-13 n.m.r. spectral analysis consisted of making a minimum number of hypotheses about expected structure-to-spectra relationships (8). By then comparing spectra to known structure for a series of D-glucans, we attempted to establish the validity of these hypotheses and to establish how diverse a structural difference could be accommodated The hypotheses were as follows. Firstly, that each polymer could be considered as an assembly of independent saccharide monomers. Secondly, that these hypothetical saccharide monomers would be 0 alkylated (0 -methylated) in the same positions as the actual saccharide linked residues (it had previously been established that 0-methylation of any a-D-glucopyranosyl carbon atom position resulted in a down-field displacement of vlO p.p.m. for the associated resonance). Thirdly, that each differently substituted residue would have a completely different set of chemical shift values for each carbon atom position (different from the unsubstituted saccharide) but that only the carbon atom positions involved in inter-saccharide linkages would have A6 greater that 1 p.p.m. And, fourthly, that the hypothetical 0-alkylated residues would contribute resonances to the total spectrum proportional to their mole ratio in the polymers. 

Also referred to as endo-l,4-j8-glucanase and carboxy-methyl cellulase, this enzyme [EC 3.2.1.4] catalyzes the endohydrolysis of l,4-j8-D-glucosidic linkages in cellulose. The enzyme also catalyzes the hydrolysis of 1,4-Unkages in /3-D-glucans also containing 1,3-Unkages. 

Figure 3 shows the structure of the hemicellulosic polysaccharides obtained from the bran cell wall preparations. These structures were deduced from the results of the methylation analysis of purified fractions (13). In contrast to the endosperm cell wall, no / -l,3-,l,4-glucan was obtained from... 

D-glucans by methylation and hydrolysis confirmed their structure, but indicated that the degree of branching in the more highly branched samples was somewhat lower than estimated by 13C-n.m.r. spectroscopy.120... 

Enzymic hydrolysis of dextrans has provided information both on the linkage types and the disposition of different linkages as established by methylation. Since the publication of the earlier article,1 enzymic studies on Leuconostoc dextrans have continued, and investigations of Streptococcus a-D-glucans have shown that there are significant, structural differences between some of these and those of Leuconostoc spp. Reviews on dextrans have appeared.419,420... 

The cell-wall j3-D-glucan fractions, insoluble in alkali and acid, from wild and from a mutant S. cerevisiae have been compared. Methylation analysis indicated more 1,3- and 1,3,6-linked D-glucosyl residues, and fewer 1,6-linked in the latter. The wild type was hydrolyzed less by exo-(l- 3)-/3-D-glucanase and more by endo-(l -> 6)-/3-D-glucanase than was the glucan from the mutant, consistent with the methylation data.4733... 

E3.4 Determining the Degree of Methylation and Acetylation of Pectin E3.5 Quantitative Determination of (3-Glucan Content... 

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