INTERCONVERSION OF SUGARS 



the formation of disaccharides which are then transformed into 

 polysaccharides, or whether the transference of the sugar residues 

 can be direct to the polymer. 



With the knowledge available at present, it should not be 

 very long before many other polysaccharides are synthesized in 

 vitro. Cellulose, chitin, xylan, mannan, and galactans contain- 

 ing a single sugar should prove easier to synthesize than mixed 

 polymers like hyaluronic acid or chondroitin sulfate, which, in 

 addition to galactosamine and glucuronic acid, contains sulfate 

 groups. And these in turn, seem to be simple cases compared 

 to blood group substances (2), which contain galactose, glucose, 

 hexosamines, fucose, and amino acids; or to gum arable (11), 

 where the sugar constituents are galactose, glucuronic acid, l- 

 arabinose, and L-rhamnose. 



A consideration of these complicated polysaccharides leads 

 to a digression on their role in living cells. Besides the more 

 obvious structural role of substances like cellulose and the role of 

 glucose and fructose polymers as reserve substances, it seems that 

 sometimes polysaccharides form a chemical barrier which pro- 

 tects the organism from attack. The barrier can be overcome 

 only by using the right key, that is, an enzyme which will dissolve 

 the barrier. The more unusual barriers will be those which 

 afford a greater survival value for their possessors. Examples of 

 this are numerous. Hyaluronic acid does not allow the spread- 

 ing of infectious agents in the dermal tissue, but microbes secret- 

 ing the corresponding enzyme, hyaluronidase, are not affected 

 by the hyaluronidase barrier. Spreading of the infection occurs 

 also if hyaluronidase is injected together with microbes which do 

 not have the enzyme. 



Virulent pneumococci differ from the nonvirulent by the 

 presence of a capsule which surrounds the cells. In this case, the 

 polysaccharide capsules, which are formed by different combina- 

 tions of sugars, uronic acids, and hexosamines (6), appear to be 

 resistant to the enzyme equipment which forms a part of the 

 host's anti-infectious mechanism. 



The plant gums have been thought to represent a protec- 

 tive mechanism by which the injured parts of the plant are sealed 



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