4\ Carbon Metabolism 



Part I 

 Introduction 



T 



_l-he sheer bulk of the reported investigative work on 

 carbon metabolism dictates some subdivision of the topic for the sake 

 of convenience. In this and the two succeeding chapters we are con- 

 cerned with the principal transformations of carbon compounds 

 brought about by fungi, excluding those primarily important in the 

 metabolism of nitrogenous compounds (Chapter 8) and a few which 

 are better considered in conjunction with respiration (Chapter 7). 



Broadly considered, the physiological problems of carbon metabo- 

 lism are two: the conditions under which a compound is utilized, and 

 the conditions under which a compound is manufactured by the cell. 

 These lead to two corresponding biochemical problems, the pathway 

 of breakdown and the pathway of biosynthesis. The natural occur- 

 rence of compounds and processes is also of interest. For any class of 

 compounds the information is usually incomplete; thus, the physiology 

 of acid formation is better known than are the biosynthetic pathways 

 involved, and very little solid information on the breakdown of the 

 acids is available. Many interesting compounds are known so far 

 largely as curiosities, since neither their physiological significance nor 

 their biosynthesis has been explored; it seems warranted, however, to 

 include at least some examples of these in a discussion of fungus 

 physiology. 



Because so much work has been done on the metabolites which 

 accumulate in large amounts, it is salutary to recall that probably 

 most fungi in culture form cell material and carbon dioxide exclu- 

 sively. Thus, of 40 basidiomycetes investigated by Whi taker (21), 



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