492 ENZYMES 



The net result is, therefore, that, as before — - 



2 {CeHiPe = CO, + CH3CHO + CaH^Oa} . . (i) 



2CH3CHO + H2O = CH3COOH + CH3CH2OH . . (2) 



On combining these two equations — 



2C6H12O0 + H2O = 2CO2 + 2C3H8O3 + CH3COOH + CH3CH2OH 



Thus it is seen that according to the conditions, Sacc- 

 haromyces cerevisece growing on a sugar substrate can bring 

 about three distinct types of fermentation : — 



(i) CeHiPe = 2C2HeO + 2CO2. 



(2) CgHiaOg = CH3CHO + C3H5(OH)3 + CO2. 



(3) 2C6H12O6 + H2O = 2C3H8O3 + CH3COOH + CH3CH2OH + 2CO2. 



CO-ENZYME OF ZYMASE. 



Harden and Young * showed that if yeast juice is dialysed 

 or subjected to ultrafiltration it can be separated into two 

 constituents ; a non-dialysable enzyme which does not pass 

 through the filter and a dialysable constituent, the co-enzyme, 

 which does pass through the filter. The enzyme constituent 

 is thermolabile, whilst the co-enzyme is thermostable. 



Neither of these two substances is able alone to bring 

 about alcoholic fermentation, but when reunited after separa- 

 tion by dialysis or ultrafiltration, the mixture is able to ferment 

 sugar even if the co-enzyme has been boiled. 



The nature of the co-enzyme is unknown ; Neuberg and 

 Schwenk f found that washed zymin could be reactivated by 

 the addition of a mixture of a-ketonic acids and phosphate, 

 whilst Harden % found that zymin prepared from top fer- 

 mentation yeast deprived of its co-enzyme by washing, was 

 reactivated by sodium and potassium pyruvate, or by alde- 

 hydes, provided potassium ions arepresent. If sodium pyruvate 

 is used alone no activation results, but a mixture of sodium 

 and potassium pyruvate, or the latter salt alone, are effective. 

 With respect to bottom yeasts, Neuberg § considers that 

 ketonic acids are of most importance, and attaches but little 

 significance to the potassium ions. According to Neuberg 



* Harden and Young : " Proc. Roy. Soc," B., 1906, 78, 369. 

 t Neuberg and Schwenk : " Biochem. Zeit.," 1915, 71, 135. 

 X Harden : " Biochem. Journ.," 1917, 11, 64. 

 § Neuberg : " Biochem. Zeit.," 191S, 88, 145. 



