O. Nitrogen Nutrition 



and 

 Metabolism 



w, 



ritli the exception of certain problems in amino 

 acid biosynthesis, the nitrogen metabolism of the fungi has been rela- 

 tively neglected. Numerous surveys of nitrogen nutrition have been 

 made, unfortunately too often without a clear conception of the physio- 

 logical problems involved. As will be seen, little is known of the 

 mechanism of nitrogen assimilation into amino acids and proteins, 

 the synthesis of specific peptides, and the metabolism of purines and 

 pyrimidines. 



There is no optimum amount of nitrogen for a culture; the demand 

 depends in the first instance upon the carbon supply, but in principle, 

 at least, any factor may change the apparent optimum concentration 

 of the nitrogen source. The dependence upon carbon is illustrated 

 in Figure 1; in this organism, Aspergillus niger, enough is known of 

 other cultural factors so that a strict proportionality between carbo- 

 hydrate supply and nitrogen demand can be demonstrated (496). 



No single pattern of nitrogen assimilation can be described to apply 

 to all fungi. In general, however, inorganic or organic nitrogen is 

 taken up rapidly during the phase of growth. Even in this phase, 

 however, there may be a back movement of ammonia nitrogen from 

 the cells to the medium (211), reflecting the permeability of the cell 

 to ammonia. Certain enzymes also begin to appear in the medium 

 during this period (115, 278), and in at least some organisms amino 

 acids and other soluble nitrogen compounds are liberated (139, 181, 

 374, 413). The major liberation of proteins and other nitrogenous 



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