Polysaccharides fragmentation analysis

The classical techniques of stractural analysis of polysaccharides, namely, fragmentation analysis (for example, by acid hydrolysis), methyl-ation analysis, and periodate oxidation (for reviews, see Refs. 1-3) have... 

A reliable proof that a given polysaccharide is a heteroglycan and not a mixture of homoglycans is afforded by the isolation, by fragmentation analysis, of a disaccharide containing two different monosaccharide units. Precautions to avoid reversion (see below) must be observed this difficulty is readily circumvented by the use of dilute solutions of the carbohydrate. 

The structures of oligosaccharides and polysaccharides are usually determined by a combination of methods specific enzymatic hydrolysis to determine stereochemistry and produce smaller fragments for further analysis methylation analysis to locate glycosidic bonds and stepwise degradation to determine sequence and configuration of anomeric carbons. 

Approximately 400 different glycosyltransferases are necessary in order to ensure the synthesis of those bacterial polysaccharides whose structures have thus far been elucidated. This estimate is based on the results of an analysis of the structures, made in order to ascertain how many different disaccharide fragments are present. An example of such an analysis is shown in Table V for the disaccharide sequences L-rhamnopyranosyl-D-galacto-pyranose, D-mannopyranosyl-L-rhamnopyranose, and D-galactopyranosyl-D-mannopyranose that are characteristic for the O-specific polysaccharides of Salmonella serogroups A, B, D, and E, the objects of many biosynthetic studies. Full details of similar analyses for other disaccharide sequences will be published elsewhere, as the resulting Tables are too voluminous for inclusion in this Chapter, but the most interesting results are summarized in Tables VI and VII. 

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