ALCOHOLIC FERMENTATION 260 



free fi'om all activators ; Holozymase (or paiiz^inase) to 

 designate the complete system of zymase plus the acti- 

 vators ; and Apozymase, which is the holozymase free 

 from CO -enzyme but still containing the magnesium salts. 

 That is, 



Holozymase =Zymase-|-Mg+ Co-enzyme 

 Apozymase = Zymase +Mg. 



Zymase is, itself, a complex mixture of several enzymes 

 (see p. 275 et seq.). 



Mechanism of Alcoholic Fermentation. — In elaborating 

 a mechanism to account for alcoholic fermentation the 

 following facts have to be considered : — 



(1) All the compounds which are produced in a 

 normal alcoholic fermentation can be derived from 

 molecules containing three carbon atoms, which may be 

 obtained by a preliminary split of the glucose molecule 

 into two such fragments following phosphorylation as an 

 essential step. 



(2) Acetaldehyde has been demonstrated, by fixation 

 with sulphite or dimedon, as an intermediate. 



(3) Pyruvic acid is also regularly formed, as shown 

 by its fixation by the use of p-naphthylamine. 



(4) Neuberg isolated from yeast the enzyme carbo- 

 xylase, which splits pyruvic acid (and «-keto -acids in 

 general) into carbon dioxide and acetaldehyde. 



(5) Glycerol is always formed to the extent of 3 to 

 4 per cent, in normal fermentations, and under certain 

 conditions large quantities of it are formed. 



(6) Usually none of the intermediates is left, and 

 the end products are almost entirely carbon dioxide and 

 alcohol in equivalent quantities. 



A considerable number of theories have been pro- 

 posed to account for all these facts, of which the three 

 most important are those due to Kluyver, Neuberg, 

 and Mj-erhof ; the last of these is the one now generally 

 accepted. 



