1923] 



KLOTZ — NITROGEN METABOLISM IN FUNGI 



301 



molecule into its very reactive fragments which would unite 

 with the ammonia to form amiDO acids from which the proteins 

 would arise. 



Czapek ('02), in his extensive cultural studies with Aspergillus 

 niger, used cane sugar as a carbon source and an almost all- 

 inclusive list of possible N sources. Judging from the substances 

 used, the per cent of N utilized, the appearance of the culture, 

 and the dry weights of the fungous crops obtained in the presence 

 and absence of sugar, he concluded that proteins are most easily 

 synthesized from the amino acids and from those substances 

 which most nearly resemble the amino acids. For example, the 

 high utility of acetamid as an N source is explained by the fact 

 that its structure approaches that of an amino acid. 



"Die Eiweissynthese wird demnach aus Aminosauren (und Di- 

 aminosauren) am leichtesten und ausgiebigsten bewerkstelligt, wenn 

 man gleichzeitig eine gute Kohlenstoffquelle, z. B. eine Zuckerart, 

 darreicht. Es vermag also der Schimmelpilz aus irgend einer be- 

 liebigen Aminosaure viel leichter alle ubrigen, welche als Bausteine 

 des Eiweissmolekuls in Betracht kommen, zu bilden, als erst aus 

 anderen Stickstoffverbindungen Aminosauren synthetisch aufzu- 

 bauen. Man kann ferner annehmen, da die Aminosauresynthese als 

 Vorstufe zur Eiweissbildung anzusehen ist, dass aus jenen Stoffen, 

 welche am besten als N-Quellen dienen (hier besonders den Oxyfett- 

 sauren), auch am leichtesten die Synthese der Aminosauren bewerk- 

 stelligt werden kann — ein Gedanke, welcher in ferneren Unter- 

 suchungsreihe noch weiter verfolgt werden soil." 



In a later experiment he used asparagin as the N source and 

 varied the carbon source, employing in all 24 carbohydrates, 

 higher alcohols, and organic acids. From the dry weights ob- 

 tained, the extent of utilization of the asparagin, and the ap- 

 pearance of the culture, he supports the r Eiweissregeneration 

 aus Asparagin und Kohlehydraten ' ' hypothesis of Pfeffer (72) 

 and Borodin ('78), stating that protein synthesis is essentially 

 the same in Aspergillus niger as in the seedlings of flowering 

 plants. Loew also speculated on the significance of asparagin 

 in nutrition, saying that a fungus fed this and sugar forms an 

 aldehyde of aspartic acid which is then condensed to make the 

 protein molecule. 



The classic chemical work of Emil Fischer (K. Hoesch, '21), 

 following closely upon that of Czapek, threw much light upon the 

 constitution of the protein molecule and its manner of synthesis. 



