Polysaccharides disaccharide fragments

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. 

The disaccharide fragments listed in this Table are not found in the polysaccharides of Gram-positive cell-walls. For references on the structures of O-specific and capsular polysaccharides mentioned in this Table, see Refs. 98 and 276. b The total number of isomeric, disaccharide fragments identified in different polymers is shown in parentheses. 

The list of the most common monosaccharide components of bacterial polysaccharides, shown in Table VI, includes the sugars that were found at the nonreducing end of nine or more different disaccharide fragments of the polymers. The right-hand column of the Table, which shows the total number of such fragments, gives an estimate of the number of different glycosyltransferases that use the activated form of the monosaccharides as... 

Total Number of Isomeric Disaccharide Fragments of the Polysaccharides Composed of the Most Common Monosaccharides"... 

In 1967, Heidelberger, Stacey et al. reported the purification, some structural features, and the chemical modification of the capsular polysaccharide from Pneumococcus Type I. Difficulties of direct hydrolysis of the polysaccharide were overcome and it was possible to identify some of the fragments in the hy-drolyzate. At least six products resulted from nitrous acid deamination. Two were disaccharides, which were identified, and sequences of linked sugar units were proposed. As modification of the polysaccharide decreased the amounts of antibody precipitated by anti-pneumococcal Type I sera, the importance of the unmodified structural features in contributing to the specificity of the polysaccharide was indicated. 

Saliva begins the process of chemical digestion with salivary amylase. This enzyme splits starch molecules into fragments. Specifically, polysaccharides, or starches, are broken down into maltose, a disaccharide consisting of two glucose molecules. Salivary amylase may account for up to 75% of starch digestion before it is denatured by gastric acid in the stomach. 

Polysaccharide (starch) Amylase Fragment polysaccharides into disaccharides (maltose) Salivary glands pancreas Mouth stomach small intestine... 

In the course of their structural studies of polysaccharides, the Aspinall group isolated several oligosaccharide fragments and characterized them by comparison with specifically synthesized samples. Disaccharides made for this purpose were 2-0-/ -D-xylopyranosyl-D-xylose, its monomethyl derivative with the substituent at 0-3 of the nonreducing moiety, and 2-0-/ -D-xylopyranosyl-L-arabinose. A biosynthetic investigation led to the establishment of the sugar ring size of natural uridine 5 -(L-arabinofuranosyl pyrophosphate). 

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