TYPE SPECIFIC POLYSACCHARIDES 121 



serum will react with any pneumococcus irrespective of type. 

 Further, the serum prepared against the intact cell will 

 precipitate the Type I polysaccharide, but not polysaccharides 

 prepared from other types, while the serum prepared against 

 the protein fraction will not precipitate any of the poly- 

 saccharides. It seems, then, that the antigen is the protein 

 part of the cell, but the presence of the polysaccharide 

 confers specificity upon the antibody response. This suggests 

 that the 32 pneumococcal types differ in the nature of the 

 polysaccharides composing the capsules. The structures of 

 several of these substances have been worked out; the Type III 

 polysaccharide consists of glucose and glucuronic acid residues 

 linked into chain formation as follows: — 



COOH OH 



CH2OH J 0, ^ A k . 9" 



Y— f^ OH CHgOH r""0 



OH COOH 



Energy stores 



In mammalian tissues, energy is stored in the glycogen 

 deposits while in plant tissues storage occurs mainly in the 

 form of starch. Bacteria are known to accumulate reserves 

 of polysaccharide material within the cell, but few studies 

 have been made as yet on the nature of these stores. For 

 example, when Esch. coli is allowed to metabolise glucose in 

 excess, then polysaccharide formation occurs within the cell, 

 but this material is itself metabolised as soon as the external 

 glucose is exhausted. 



FOR FURTHER READING 



Introduction to Carbohydrate Biochemistry, Bell, D. J. 



(Univ. Tut. Press). 



Bacterial Metabolism, Stephenson, M. (Longmans). 



