98 PHYSIOLOGY OF YEASTS 



This question, as we have seen, is extremely complex; the question 

 is being studied but instead of becoming simpler becomes more com- 

 plicated. 



Lebedew l has later restated his idea of the mechanism of alco- 

 holic fermentation as follows: 



4 C 6 Hi 2 O 6 = 8 C 3 H 6 O 3 . 



Glyceraldehyde 

 4 C 3 H 6 3 - 4 H 2 = 4 C 3 H 4 3 . 

 4 C 3 H 4 3 = 4 C 2 H 4 O + 4 CO 2 . 

 4 C 2 H 4 + 4 H 2 = 4 C 2 H 5 -OH. 



Dioxyacetone 



4 C 3 H 6 O 3 + 4 RHPO 4 = 4 G 3 H 5 O 2 RPO 4 + 4 H 2 0. 

 4 C 3 H 5 O 2 RPO 4 = 2 C 6 H 10 O 4 (RPO 4 ) 2 . 

 2 C 6 H 10 04(RP0 4 ) 2 + 4 H 2 = 2 C 6 H 12 O 6 + 4 RHPO 4 . 

 2 C 6 H 12 6 = 4 C 3 H 6 3 , etc. 



Neuberg 2 has studied the possibilities of intermediate compounds 

 in alcoholic fermentation. He believes that the CO 2 which appears 

 in alcoholic fermentation is split off from (CH 3 CO.COOH) pyruvic 

 acid. He found that it took from 2-8 seconds for CO 2 to be formed in 

 yeast maceration + CH 3 CO.COOH while it took from 2-3 hours for 

 it to be formed from yeast + glucose. Neuberg and his coworkers 

 also used oxalacetic acid and found that yeast would change this to 

 two molecules of CO 2 and one molecule of CH 3 CHO. Hydroxypyruvic 

 acid yielded CO 2 and glycoaldehyde, a ketobutyric acid yielded pro- 

 pionaldehyde and C0 2 along with some propyl alcohol. They find 

 that the cleavage of pyruvic acid takes place 2000 times more rapidly 

 than the complete fermentation of sugar. Neuberg and Kut then 

 argue that two processes are involved in alcoholic fermentation. 

 First, one class of enzymes hydrolyzes the C 6 molecule into C 3 chains. 

 Secondly, another class of enzymes (carboxylase) breaks the C 3 chains 

 up into C 2 and Ci compounds. In further researches Neuberg has 

 shown that yeasts possess an enzyme which decomposes pyruvic acid 

 into acetaldehyde and C0 2 . Acetaldehyde is readily reduced during 

 fermentation to ethyl alcohol. From this it seems probable that 

 aldehyde is an intermediate compound in fermentation. Neuberg 

 and Reinfurth showed that if fermentation was carried out in the 

 presence of NasSOs considerable amounts of aldehyde could be ob- 



1 Lebedew, A. and Griaznoff, N. Ueber den Mechanismus der alkoholischen 

 Garung. II. Chem. Berichte, 45 (1912), 3256-3272. 



2 See bibliographical index for complete list of Neuberg's publications on 

 sugar-free fermentations. 



