Other Homopolysaccharides

The best known homopolysaccharides are derived from o-glucose and known as glucans. Glucose has a number of reactive sites and a wide variety of polymers formed utilizing combinations of these reactive sites are found in nature. We have already visited the two most well-known members of this group—cellulose and starch containing amylose and amylopectin. Here we will visit some other important members. 

Other examples of exocellular homopolysaccharides whose biosynthetic process has been investigated include D-mannuronan,204,205 an intermediate in the biosynthesis of bacterial alginic acid (mentioned in Section III,l,c), and bacterial cellulose. 

Figure 1 represents the general structure of Salmonella lipopolysaccharides. They contain an external polysaccharide, the O-antigenic chain, and an innermost component, termed lipid A. O-chain and lipid A are linked to each other by an oligosaccharide referred to as the core. O-Specific Chains. As indicated in Figure 1, O chains are in general made up of repeating units of di-, tri-, or higher oligosaccharides. In rare cases the O-chain is a homopolysaccharide. The structure of the O-chain is unique to each bacterial serotype great diversity is encountered in the structures of O-chains.

In order to provide access here to information about other microbial polysaccharides, there follows a short review of reviews. The Chemical Nature of Bacterial Antigens is a source of information on the earlier work, and this was followed by two reviews - in the present Series in one of these, the bacterial homopolysaccharides were discussed and some of the more complex products were mentioned. A wide review of mucopolysaccharides and mucoproteins included references to many bacterial polysaccharides, and, subsequently, an account of the specific polysaccharides of the Gram-positive Pneumococcus, and of dextrans, levans, and products of Gram-negative forms appeared. There followed a comprehensive review of pneumococcal polysaccharides, and an account restricted to products of Mycobacterium tuberculosis appeared in 1948. A broad coverage was provided in 1950, in this case the products of pathogenic species being dealt with more particularly this work encompassed the basis of the more... 

The preferred source materials for preparation of monosaccharides are the homopolysaccharides built of repeated residues of a single sugar. A more-complex natural product may be used if the desired monosaccharide can be selectively liberated by hydrolysis, or if other sugars present in the hydrolyzate can be conveniently eliminated, for example, by fermentation. Alternatively, a more-complex... 

Lack of specificity of an enzyme for the linkage hydrolyzed in a mixed-linkage homopolysaccharide has already been mentioned (see p. 269), Rhizopus arrhizus laminaranase being able to split both (l->3)- and (l- 4)- -D-glucosidic linkages. The possibility that such an action may explain results difficult to account for on any other basis should always be borne in mind. 

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