BIOSYNTHESIS OF AMINO ACIDS 265 



the tricarboxylic acid cycle. Glutamic decarboxylase, presumably 

 yielding y-aminobutyric acid, has been detected in Penicillium chryso- 

 genum (201) and Endomycopsis vernalis (290). 



It might be at first glance surprising that proline, a ring compound, 

 is generally an excellent source of nitrogen for fungi (275, 278, 409, 

 412). The answer conceivably lies in a ready conversion of proline 

 to glutamic acid, i.e., reversal of the steps in the synthesis of proline 

 from glutamate (p. 268). 



Hydrolysis of Acyl Amino Acids and Amides. Nitrogen-acylated 

 amino acids are hydrolyzed, liberating the free amino acid, by prepara- 

 tions from Aspergillus spp. and Penicillium spp. (263, 364, 389, 405). 

 Although these reactions may be referred to as acylase activity, it must 

 be realized that there is in fungi no clear separation of acylases, ami- 

 dases, and peptidases, all of which act on the — C — O — N< bond. 



Hippuricase (histozyme) splits hippuric acid (N-benzoylglycine) to 

 benzoic acid and glycine. Its identity and relation to other acylases 

 and to peptidases is still obscure; certain other N-benzoylated L-a-amino 

 acids are attacked (325). It has most recently been studied in Peni- 

 cillium spp. (263, 456); reports of its occurrence in other fungi are 

 reviewed by Leuthardt (325). 



Asparaginase, hydrolyzing asparagine to aspartic acid and ammonia, 

 has received some attention, although it has not been purified. Ac- 

 tivity is found in Aspergillus niger (467), Penicillium spp. (134, 456, 

 535), Microsporum spp. (51), and Piricularia oryzae (260). The opti- 

 mum pH is about 8 (32, 51, 467). The enzyme of A. niger is liberated 

 into the medium only on autolysis (33), is not easily solubilized in 

 sand-ground preparations (35), is unstable (36, 630), and is formed in 

 cells grown on a synthetic medium (467). 



Amidase activity against glutamine is found in yeast, bacteria, and 

 higher animals (630); it is probably common in the fungi, but has been 

 reported so far only in Neurospora crassa (523). 



Several early reports, reviewed by Foster (163), suggest that fungal 

 enzymes also act on aliphatic or aromatic amides, e.g., acetamide and 

 benzamide. In view of the negative results of Schmalfuss and Mothes 

 (467) it is perhaps best to suspend judgment, although aliphatic amides 

 are hydrolyzed by Torula utilis (630). Penicillinase and penicillin 

 amidase, both acting on amide linkages, have been mentioned briefly 

 in Chapter 6. 



4. BIOSYNTHESIS OF AMINO ACIDS 



The formation of amino acids by fungi may be considered for our 

 purposes from three aspects: (1) the entrance of nitrogen into the 



