CARBOX SOURCES 



141 



two fungi is not proof that the reaction mechanism is the same in both 

 instances. Yeast and certain species of Fusarium produce alcohol, but 

 the pathways from glucose to alcohol appear to be different. The 

 mechanism of carbohydrate dissimilation by Fusarium lini, when grown 

 upon a nitrate medium, is believed to take place as shown in scheme V. 

 An essential feature of this scheme is the formation of pyruvic acid from 

 both pentoses and hexoses. The intermediate steps in this biosynthesis 

 by Fusarium lini have not been elucidated. A portion of the hydrogen 

 derived from the dissimilation of carbohydrate is enzymatically trans- 

 ferred and used for the reduction of nitrate ion which acts as a hydrogen 

 acceptor. The nitrite produced inhibits the carboxylase enzyme system 

 which transforms pyruvic acid into carbon dioxide and acetaldehyde. 

 Pyruvic acid does not accumulate in the culture medium when ammonium 

 nitrogen is used. 



Scheme V. The Pathway of Hexose and Pentose Utilization by Fusarium lini 



Grown on Nitrate Medium 

 (Courtesy of Wirth and Nord, Arch. Biochem. \ : 155, 1942. Published by permis- 

 sion of Academic Press, Inc.) 



Acceptor 

 (Nitrate) 



Nitrite 



I 



Carboxylase system 



Hydroxylamine 

 + 

 ->- Pyruvic acid ^- Alcohol 



X reduction 

 Amino acid 



Utilization 



Hexoses 



Pentoses 



Pyruvic acid is the key intermediate compound formed in the dis- 

 similation of hexoses and pentoses by F. lini. The transformation of 

 pyruvic acid into alcohol by F. lini and yeasts appears to follow the same 

 pathway and to require the same coenzymes, cocarboxylase and code- 

 hydrogenase I. 



The anaerobic dissimilation (fermentation) of glucose by yeast and 

 the comparable process in muscle (glycolysis) have been intensively 

 studied. These are perhaps the best understood of all metabolic proc- 

 esses. Although it does not function in glucose dissimilation by F. lini in 

 the same way as in yeast, phosphate plays a role in all these transforma- 

 tions until pyruvic acid is formed. Many investigators have contributed 



