108 PHYSIOLOGY OF THE FUNGI 



utilization, while Cznpek believed that amino acids were utilized directly. 

 Both processes arc doubtless involved, and only prolonged study of 

 specific fungi and various nitrogen sources will permit elucidation of these 

 questions. 



One of the main uses of nitrogen is in the synthesis of proteins. With 

 the exception of certain amino acids (primary amino acids) and ammonia, 

 most nitrogen sources undergo modification before entering the synthetic 

 metabolic pathways. Nitrates, nitrites, and hydroxylamine are pre- 

 sumably reduced to ammonia before assimilation. Those amino acids 

 (secondary amino acids) which do not enter directly into the metabolic 

 pathways leading to the synthesis of protein are probably deaminated. 

 Burk and Horner (1939) have listed the types of deamination performed 

 by fungi as follows: 



1. Deamination by hydrolysis: 



H2O 

 R— CH(XH.:)— COOH > R— CH(OH)— COOH + NH3 



2. Deamination by hydrolysis followed by decarboxylation: 



H2O 

 R— CHCNHo)— COOH > R— CH2OH + CO2 + NH3 



3. Oxidative deamination: 



MO, 

 R— CHCNHa)— COOH > R— CO— COOH + NH, 



The production of higher alcohols, "fusel oil," is due to hydrolytic 

 deamination and decarboxylation of various amino acids, especially 

 leucine, which yields isoamyl alcohol. Various species of filamentous 

 fungi, especially those which produce alcohol, are capable of the same 

 reactions. The following amino acids are converted by yeasts into alco- 

 hols having one less carbon than the parent amino acid: leucine, isoleucine, 

 phenylalanine, trytophane, and valine. Wirth and Nord (1942) indicate 

 that Fusarium lini oxidatively transforms alanine into pyruvic acid. 

 For further information on the process of deamination by yeast, see Thorn 

 (1937). The process of deamination releases nitrogen in the form of 

 ammonia, which is utilized by most fungi. 



It seems probable that the synthesis of amino acids is the next step in 

 protein formation. The formation of primary amino acids may result 

 from the reaction of ammonia with certain alpha-keto acids (pyruvic, 

 oxalacetic, and ketoglutaric) ; this is essentially the reverse of oxidative 

 deamination. This process may be fo.'mulated as follows: 



R— CO— COOH + NH3 -> R— C(=NH)— COOH + H. -^ R— CHCNH.)— COOH 



In addition, yeasts are able to add ammonia to fumaric acid to form 

 aspartic acid (Haehn and Leopold, 1937). The role of the four-carbon 

 dicarboxylic acids in nitrogen assimilation may be explained on the basis 

 that these acids are transformed into kcto acids. Brian et al. (1947) have 

 assumed that those fungi, such as Phycomyces hlakesleeanus and Myro- 



