1923] 



KLOTZ — NITROGEN METABOLISM IN FUNGI 



309 



Like Brenner ('11), Puriewitsch ('12) reverts to the view of 

 Czapek that a-amino acids serve directly as materials for protein 

 synthesis and are therefore the most favorable N sources. This 

 investigator attempted to clarify the problem of protein synthesis 

 by determining the energy required for the assimilation of the 

 different nitrogenous compounds. The energy was estimated 

 by measuring the CO * evolved per unit of dry weight of the fungus 

 produced. Aspergillus niger was the organism employed. The 

 CO j was swept out by a stream of air into tubes containing KOH 

 and weighed. Used with dextrose, the amino acids, methyl 

 urea, KSCN, acetamide, urea, and methylamine gave a low 



rati o 



CO 



dry wt. ' 



while KNO,, ethylamine, phenylurea, guanidine, 



protein, and peptone gave higher ratios, showing that they 

 required more energy for their assimilation. Ammonium salts 

 occupied about a middle position. Some of the N compounds 

 were also tried with malic, succinic, and tartaric acids as 

 carbon sources in the place of glucose. Although the ratios ob- 

 tained were somewhat higher than with the sugar, the same 

 general order of assimilability of the N compounds was obtained. 

 However, with malic acid the NH (l salts were superior to glycine, 

 and KNO j almost as good. With respect to the C sources the 

 ratio increased in this order: dextrose, succinic acid, malic acid, 

 and tartaric acid. It is difficult to understand the interpretation 

 of Puriewitsch and his inclination towards Czapek's view, when 

 one examines his data for peptone, which gave a high ratio for 

 all C sources. 



Dox and Maynard ('12) cultured Aspergillus niger and Penicil- 

 iium expansum in a liquid medium having sucrose and ammonium 

 acid tartrate as the C and N sources, and at the end of each week 

 made determinations of the total and ammonia N of the medium. 

 They found that both forms of N decreased rapidly during the 

 first week of growth, and then during the next 5 weeks increased 

 to a constant quantity. The N retained in the mycelium after 

 this equilibrium had been established was thought to be " some 

 chitin-like substance or glucosamine complex which does not 

 undergo autolytic change." Similar results were obtained when 

 KNOi was the N source. Dox (13) continued this work with 



