116 SPECIFIC NATURE OF CATALYTIC ACTION 



stance only ; it may attack many hundreds if only they all possess 

 a given molecular and stereo-identical grouping, and it is this 

 relationship upon which the specific action is based. Also the 

 extent of action depends on the group attacked. Thus both 

 invertase from yeast, and emulsin from bitter almonds, attack 

 the glucoside, amygdalin ; but invertase only detaches a molecule 

 of glucose, leaving the remainder untouched, while emulsin, attack- 

 ing a different grouping, breaks the amygdalin up into benzaldehyd, 

 hydrocyanic acid, and glucose. Other natural glucosides, not 

 possessing the particular grouping attackable by invertase, are 

 resistant to that enzyme, and are attacked only by emulsin. 



An interesting fact in the case of the cell, showing physiologi- 

 cal adaptation to environment and nutrition, is that the action 

 depends upon the food supply ; the cells forming in all probability 

 enzymes to suit the configuration of the molecules at their dis- 

 posal. Thus, aspergillus cultivated on a nutrient medium con- 

 taining lactose or /3-methyl-galactosid acquires the property of 

 hydrolysing these, while if grown upon a-methyl-galactosid the 

 property is acquired of attacking this substance. 



The outcome of these investigations appears, then, to be that 

 by specific action must be understood entire conformity between 

 the particular enzyme and a corresponding molecular grouping 

 or structural arrangement in the molecule attacked, and not that 

 a single substance only is attacked by the same enzyme. 



It may perhaps, in conclusion, be pointed out that this may 

 serve to explain what sometimes seems a most fantastic distri- 

 bution of certain enzymes in nature. Thus the stomach of the 

 fish contains a milk-curdling enzyme, similar to that of the 

 mammalia, although such an enzyme never comes in contact 

 with milk, and never has in the development of the fishes. The 

 presence of such an enzyme cannot certainly be regarded as a 

 prevision of Nature for the coming mammalia, and points to the 

 fact that the milk-curdling enzyme must have other functions 

 than the coagulation of milk. Since such ferments are also 

 found in plants, it follows that they must, like the sucroclastic 

 enzymes, be adapted to some definite molecular grouping upon 

 which they act, and that milk coagulation can be but one example 

 of their activity. 



