532 



ANAEROBIC RESPIRATION 



such as pyruvic acid, forming aldehydes. Equations representing these reac- 

 tions are given later in this chapter. 



TABLE 55 CLASSIFICATION OF THE PRINCIPAL OXIDIZING-REDUCING ENZYMES AND 



ENZYME SYSTEMS 



Zymase will not act as a catalytic agent except in the presence of certain 

 co-enzymes, as shown by the following experiment. If an extract of zymase is 

 prepared and then filtered through an ultrafilter it will be found that the 

 enzyme-containing residue on the filter will not, when redispersed in water, 

 catalyze the alcoholic fermentation of a hexose. Neither will the filtrate. If, 

 however, some of the filtrate is mixed with the enzyme the reaction will pro- 

 ceed in the usual way. Evidently there is associated with zymase some dif- 

 fusable substance or substances which must be present for the operation of 

 this enzyme complex as a catalyst. Further investigation has shown that there 

 are apparently two of these filterable co-enzymes of zymase, one of which is 

 definitely known to be a phosphate, the other apparently being a crystalloidal 

 organic compound. 



2. Peroxidases are enzymes which bring about the oxidation of phenolic 

 compounds such as pyrogallol, catechol, and benzidine in the presence of hydro- 

 gen peroxide. In plant tissues such enzymes may also operate in the presence 

 of organic peroxides. The usual method of demonstrating the presence of a 



