44 THE COMPOSITION OF FUNGUS CELLS 



(78) found the total nitrogen of cultivated fungi to range from 2.27 

 per cent of the dry weight in Coprinus radians to 5.13 per cent in 

 Trichoderma lignorum; sporophores from nature had as little as 1.56 

 per cent nitrogen. These data are fairly typical, although fungi grown 

 in culture may be as high as 7.6 per cent nitrogen (115, 132). Differ- 

 ent species of Tricholoma vary from 3.1 to 7.7 per cent nitrogen (114). 



Measurements of total nitrogen are, however, not highly significant, 

 by reason of the susceptibility of the value to environmental influences 

 and its variation with developmental status. Characteristically, young 

 mycelium is higher in nitrogen than old (7); during autolysis both 

 proteins and other nitrogen compounds are liberated into the medium 

 (Chapter 1). In Aspergillus niger, the onset of sporulation is coinci- 

 dent with a decline in mycelial protein (168). 



The most important single influence on the total nitrogen content 

 is the concentration of nitrogen in the medium; an increase in the 

 amount of available nitrogen is accompanied by a significant — as much 

 as threefold — increase in cell nitrogen (78, 81, 166, 173). 



The nitrogen source used also exerts an influence on the total nitro- 

 gen of the mycelium; in general, the nitrogen content is higher when 

 ammonium salts are used than when nitrates provide the nitrogen 

 (93, 170, 173, 194). The cause of this effect is uncertain; either the 

 low pH incident upon utilization of ammonium ion reduces autolytic 

 loss of nitrogen, or the nitrate is simply less available to the cell for 

 synthesis. 



Fractionation of the total nitrogen of the cell reveals that only about 

 60-70 percent is in proteins (67, 165); still lower values have been 

 reported (99). Determination of cellular protein by calculation from 

 total nitrogen is therefore inadmissible in principle, although most 

 protein determinations have been made in this way. 



A few specific proteins have been described (20, 28, 112, 125), but 

 no general or systematic study of fungal proteins has been undertaken. 

 Michel-Durand (107) found indications of phosphoproteins in Asper- 

 gillus niger. Qualitatively, the amino acids of fungal proteins are 

 much the same as those of other proteins; surveys of the amino acids 

 in hydrolyzates of Aspergillus flavus (127), Penicillium chrysogenum 

 (135), Ustilago zeae (32), and Venturia inaequalis (124) have been 

 made by chromatography of the acid hydrolysate, and indicate a 

 general similarity among these diverse fungi, with minor qualitative 

 differences. 



Quantitative analyses of the amino acids in hydrolysates of cellular 

 material of fungi and actinomycetes (168, 191) similarly do not reveal 



