ENERGY SUPPLY OF THE CELL 51 



amounts when the acet aldehyde is ^'trapped/' i.e., 

 combined with NaHSOs to a compound which does not 

 give the above reaction. This process has been used 

 commercially to manufacture glycerol from sugar. The 

 general equation in this case is 



C6H12O6 = C3H8O3 + CH3-CH0 + CO2. 



There is still another possibility of reactions hidden 

 in the yeast mechanism: acet aldehyde might act as a 

 hydrogen donator as well as acceptor; the result is 

 the formation of acetic acid: 



Illb: CH3C— OH - 2H = CH3COOH 



\ Acetic acid 



\0H 



Acet aldehyde hydrate 



IVe: CHs-CHO + 2H = CH3CH2OH 



This process takes place in alkaline media. Under 

 this condition, the above combination seems to be favored 

 which is really nothing but a Cannizzaro reaction 

 between two acet aldehyde molecules. This leaves no 

 acet aldehyde to act as acceptor for the hydrogen from 

 methyl glyoxal, and, as before, glyceric aldehyde takes 

 its place forming glycerol. The general equation of the 

 alkaline yeast fermentation is : 



2C6H12O6 + H2O = 



2C3H8O3 + CH3COOH + C2H5OH + 2CO2 



Glycerol Acetic acid Alcohol 



Neither the alkaline nor the sulfite fermentation of 

 yeast follow the above formulas quantitatively because 

 a certain amount of acet aldehyde will always react 

 with methyl glyoxal before being trapped, and the result 

 is a combination of two types of fermentation. 



