274 NITROGEN NUTRITION AND METABOLISM 



HC N 



G— SH 



/ 

 C N— H 



I 

 CH 2 



+ I 

 (CH 3 ) 3 - N— CH— COO- 



Ergothioneine occurs in mammalian blood and seminal fluid (182), in 

 sclerotia and in cultivated mycelium of Claviceps purpurea (40, 508), 

 and in the mycelium of several common fungi (360). Experiments 

 with carbon- 14 indicate that ergothioneine and histidine are synthe- 

 sized by the same pathway (229) and that histamine is not a precursor 

 of either (599). 



Amanita mappa fruit bodies contain an amine first called mappin 

 but now known to be identical with bufotenine; its structure, 

 5-hydroxy-N-dimethyl tryptamine (595), suggests that it is biosyntheti- 

 cally derived from 5-hydroxytryptophan, an amino acid known in other 

 organisms (353, 550) but not to date in fungi. 



6. METABOLISM OF NUCLEIC ACIDS AND THEIR DERIVATIVES 



Nucleic acids, nucleotides, and the purine bases can probably all 

 be used more or less well as sources of nitrogen by fungi (606, 607), but 

 the important aspects of nucleic acid metabolism are more narrowly 

 metabolic: the breakdown of nucleic acids and their biosynthesis. In- 

 formation on nucleic acid breakdown is rather scanty and bears almost 

 exclusively on the purine ribonucleotides. Biosynthetic studies are 

 even less definitive, and are limited primarily to nutritional studies of 

 deficient mutants. 



Catabolism of Nucleic Acids and Their Derivatives. That fungal 

 enzymes attack nucleic acids has been known for some time. In early 

 experiments liberation of phosphorus or of nitrogen bases, or utiliza- 

 tion of nitrogen for growth were the criteria, so that it is not possible 

 to specify what enzymes were involved (134, 265, 294, 357, 404). 



On comparative grounds, we may suppose that fungi, like bacteria, 

 attack nucleic acids first by nucleodepolymerase action, yielding prima- 

 rily mononucleotides. A few such activities have been shown in fungi 

 (Table 1). 



The second step in the classical pathway of nucleic acid degradation 

 is the dephosphorylation of nucleotides, yielding inorganic phosphate. 



