1/8 CARBON METABOLISM III 



coupling mechanism between substrate dehydrogenation and a poly- 

 phenol oxidase system transferring electrons to oxygen. 



Many of the quinonoid compounds of fungi are more or less in- 

 hibitory to other organisms, and it has been suggested (341) that this 

 property may confer an ecological advantage. Whether highly re- 

 active compounds like the quinones could persist long enough in 

 soil to inhibit competing bacteria and fungi is, however, somewhat 

 doubtful. 



4. DERIVATIVES OF PYRONE 



Several metabolic products may be considered together as deriva- 

 tives of 1,4-pyrone, and as related structurally to the pyranose form 

 of glucose. Kojic acid is typical: 



CO CHOH 



/ \ / \ 



HO— C GH HOHC CHOH 



II II II 



HC C— CH 2 OH HOHC CH— CH 2 OH 



\ / \ / 



o 



Kojic acid Glucopyranose 



Kojic acid was first discovered, as a product of Aspergillus oryzae, by 

 Saito (452); its structure was determined by Yabuta (568). Many 

 species of Aspergillus, but only one of Penicillium, produce it in cul- 

 ture (71, 227, 242, 303). Kojic acid is weakly antibacterial (381). 



Kojic acid is produced from most common carbon sources (71, 311), 

 although strains differ somewhat in this regard (404). The number 

 of compounds providing carbon for kojic acid synthesis is less for a 

 preformed mycelium than for growing cells (504). 



The data of Figure 8 show that, as would be expected, there is over 

 a certain range an inverse relation between nitrogen supplied to a 

 culture and kojic acid production per unit mycelial weight. These 

 data can best be interpreted as showing that kojic acid synthesis per 

 cell is maximal when growth is limited by a nitrogen deficiency, in 

 accordance with the principle that metabolites accumulate when 

 carbon is supplied in excess of that which can be incorporated into 

 cellular material. 



The formation of kojic acid is sensitive to pH; the yield from a 

 preformed mycelium declines virtually to zero as the pH is raised from 

 2.2 to 6.0 (319). Ethylene chlorhydrin increases the formation of 



