CHAPTER VII 



ENZYME ACTION 



Enzymes are classified according to their action, and not ac- 

 cording to their constitution. Although Berzelius defined cata- 

 lyzers as those substances which by their mere presence cause 

 reactions to take place between other substances, many catalyzers 

 are now known to take part in the reactions. Ostwald supposed 

 that catalyzers accelerate the rate of only those reactions which 

 go on at a slower rate in the absence of the catalyzer. It is true 

 in certain cases, however, that the catalyzer may change the 

 point of equilibrium of a reversible reaction. An example of 

 this was observed by Bodenstein and Dietz (1906) in the re- 

 versible decomposition and formation of amyl butyrate. In the 

 presence of an excess of water and amyl alcohol, the same 

 equilibrium point was reached whether the amyl butyrate or the 

 amyl alcohol and butyric acid were present in the beginning. 

 But if pancreas lipase were used as a catalyzer, 75 per cent of 

 the ester was formed or left against 85 per cent of the ester 

 when HC1 was used as a catalyzer. 



The chief distinction that is supposed to separate enzymes 

 from other catalyzers is their specificity. This is perhaps over- 

 rated, but is fairly well established in some cases. Amygdalin 

 may be decomposed by means of emulsin into HCN, benzalde- 

 hyde and dextrose. Emmerling (1901) showed that this took 

 place in three stages, each of which was accelerated by a different 

 enzyme, and that all three enzymes were present in emulsin. The 

 reversal of the process could be brought about by applying the 

 enzymes in a certain order to the separate stages. 



In case of stereoisomeres or optically active isomeres, an 

 enzyme may accelerate a reaction involving one isomere more 

 than the other. If HCN and benzaldehyde are mixed in solution 

 optically inactive benzaldehydecyanhydrin is formed, but if the 

 reaction is accelerated by means of emulsin, d-benzaldehyde- 



