5 . Carbon Metabolism 



Part II 



The Metabolism of Carbohydrates 



and Related Compounds 



T 



.he principal topic of this chapter on carbon metab- 

 olism is the metabolism of oligosaccharides and polysaccharides, 

 anticipated to some degree by the discussion of their role in carbon 

 nutrition (Chapter 3). The related compounds included are the 

 amino sugars and the polyhydric alcohols; discussion of the monosac- 

 charides is limited to a few synthetic reactions. 



1. THE METABOLISM OF MONOSACCHARIDES 



The breakdown of monosaccharides by fungi has been considered 

 separately, as respiration, in Chapter 7. A second aspect of monosac- 

 charide metabolism is the synthetic one, in which the sugar or a deriva- 

 tive of it is incorporated into larger molecules. As an example, 

 glucose in the glucolipid ustilagic acid is found by isotope studies to 

 be in part incorporated as such and in part resynthesized from triose 

 before incorporation (30). In this case and in the formation of glucose 

 polysaccharides no modification of the basic glucose molecule need be 

 assumed. However, the organism may synthesize a complex molecule 

 containing sugar moieties which were not provided in the culture 

 medium; examples include galactose in polysaccharides (Chapter 2) 

 and amino sugars in certain antibiotics (p. 122). In these processes it 

 is reasonable to assume that the new sugar or a derivative of it, e.g., 

 a phosphate ester, is made and then incorporated into the larger 



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