SPECIFICITY OF THE HYDROLYZING ENZYMES 



219 



a-methyl-d-glucoside and /3-methyl-d-glucoside. Their structures are 

 represented below: 



o o, 



HCOCHa 



\ 



HCOH\ 

 HOCH 



HCX 



I 



HCOH 



CH 2 OH 



a-methyl-d-glucoside. 



CHsOCH 



CH 3 OCH 



!\ 



HCOH 





:o o; 



CH 2 OH 



a-methyl-1-glucoside. 



HOCH 



| / 

 HC/ 



HCOH 



CH 2 OH 

 /3-methyl-d- 

 glucoside. 



HCOCH 3 

 HOCH 

 HCOH 



H 



I 



HOCH 



CH 2 OH 



/8-methyl-l- 

 glucoside. 



Of these neither a- nor /3-methyl-l-glucoside are acted upon by 

 enzymes. The a-methyl-d-glucoside is hydrolyzed by the Maltase in 

 yeast, but the j3-methyl-d-glucoside is not hydrolyzed by yeast; it is, 

 on the other hand, hydrolyzed by the enzyme Emulsin which is found 

 in the kernels of stony fruits such as' the almond and in the tissues 

 of the fungus Aspergilhis niger. But emulsin is without action on the 

 a-methyl-d-glucoside. 



Similarly, Invertase, which hydrolyzes cane-sugar to glucose and 

 fructose, will not hydrolyze maltose; maltase, which hydrolyzes maltose 

 to two molecules of glucose, will not attack cane-sugar or lactose; 

 lactase, which hydrolyzes milk-sugar, will not hydrolyze maltose or 

 cane-sugar. 



Since these various disaccharides differ from one another only in the 

 arrangement of the various groups about the central carbon-skeleton, 

 the high degree of specific interrelationship with the enzymes which 

 attack them which they display, led Emil Fischer to the view frequently 

 alluded to as the Lock-and-key Hypothesis, whereby the enzyme is 

 supposed to possess a structure which fits a particular disaccharide or 

 glucoside as the grooves of a key fit the wards of a lock. Indeed there 

 is no other way in which we can imagine a mechanism which will so 

 precisely pick out a particular arrangement of atoms and decompose 

 that one and no other. The phenomenon affords, in fact, a striking 

 confirmation of the view that these enzymes accomplish the hydrolysis 

 of the disaccharides through the formation of intermediate compounds. 



The fat-splitting ferments, or Lipases do not exhibit such extremely 

 preferential specificity. Nevertheless some measure of specificity is 

 displayed in certain instances. Thus Dakin found that in a mixture of 

 the menthyl esters of d- and 1-Mandelic Acid the menthyl-d-mandelate 

 is hydrolyzed by pancreas-lipase much more rapidly than the menthyl- 

 1-mandelate, so that the mandelic acid which results from the hydrolysis 

 is strongly dextrorotatory. 



