AROMATIC COMPOUNDS 



171 



The Biosynthesis of Aromatic Compounds. Although not all of 

 the aromatic compounds of fungi have been proved to be formed 

 from carbohydrate — some have been reported only from sporophores 

 in nature — most of them are probably so formed; this is evidenced, 

 for example, by the very high yields often obtained on synthetic 

 media (95, 128, 252). 



The origin of the aromatic ring from glucose has been investigated 

 most successfully in connection with the biogenesis of the aromatic 

 amino acids and p-aminobenzoic acid in bacteria. The current view 

 of this process may be diagrammed as follows (162): 



HO COOH HO COOH 



"V" 



! OH 



OH 



5-Dehydroquinic acid 



HO OH 



OH 



Quinic acid 



COOH 



^N 



COOH 



HO 



"Zi 5 



OH 



O ! OH 



OH OH 



5-Dehydroshikimic acid Shikimic acid 



In this scheme, an unknown compound "V" arises from carbohydrate 

 and is converted through the known materials shown to a second un- 

 identified compound "Zj", which is in turn ultimately transformed 

 into the aromatic amino acids and p-aminobenzoic acid; the known later 

 steps in the process are reviewed in Chapter 8. The initial steps of the 

 reaction sequence are not known; preliminary evidence (162) suggests 

 that the carbon chain of glucose is ruptured before incorporation of 

 glucose carbon into shikimic acid. 



A mutant of Neurospora crassa which requires p-aminobenzoic acid, 

 tyrosine, phenylalanine, and tryptophan for growth is similar in these 

 requirements to the bacterial mutants which have provided much of 

 the evidence for the scheme just outlined, and appears to be blocked 

 in the conversion of dehydroshikimic acid to shikimic acid (507). It 

 accumulates protocatechuic acid, which is then oxidized by ring fis- 

 sion (p. 174). Protocatechuic acid is known as a metabolic product 

 of Phycomyces blakesleeamis growing on a glucose-asparagine medium 



