MODE OF ACTION 465 



carbon atom, and it is found that while the a modification is 

 readily converted by maltase into glucose and methyl alcohol, 

 the j8 modification is not affected by maltase at all, but is, on 

 the other hand, hydrolysed by emulsin, which has no action 

 on the a compound. 



It would appear from this that the structure of the mole- 

 cule which is to be decomposed is the determining factor. 



Incidentally it may be mentioned that the fact that emulsin 

 and maltase are complementary in their action upon a and jS 

 methyl glucosides, enables one to classify a glucoside as be- 

 longing to the a type if it is attacked by maltase and not by 

 emulsin, or to the jS type if it is attacked by emulsin and not 

 by maltase. 



Several other examples of this selective action on the part 

 of enzymes for different optical isomers have been described 

 by Fischer and Abderhalden, who found that whereas d-alanyl- 

 d-alanine, d-alanyl-1-leucine were split up by enzymes, their 

 stereoisomers d-alanyl-1-alanine and 1-alanyl-d-alanine were 

 not. 



This peculiar dependence upon structure led Fischer to 

 suggest that the relationship which exists between the sub- 

 stance to be decomposed and its enzyme is similar to that 

 existing between a lock and its key ; or, in other words, unless 

 the molecular structures of the two substances fit each other 

 no interaction can take place. 



These facts give strong support to the theory of the 

 formation of some sort of compound between the enzyme and 

 the substrate. 



It should, however, be noted that the action of enzymes is 

 not entirely specific, inasmuch as the one and the same enzyme 

 may be able to hydrolyse two or more substances. Thus mal- 

 tase is able to hydrolyse both maltose and a-methyl glucoside ; 

 and emulsin is able to decompose j8-methyl glucoside, ^- 

 methyl galactoside, milk sugar, amygdalin (the glucoside of 

 bitter almonds, and with which it is primarily associated in 

 nature), arbutin, salicin, and coniferin and most naturally 

 occurring glucosides. 



The specific nature of the interaction between enzymes and 



30 



