62 GENERAL AND PHYSICO-CHEMICAL. 



and d-galactose, and of the ketohexoses only one, d-fructose are fer- 

 mentable; and then that the synthetically prepared stereoisomeric 

 glucosides behave differently with the enzymes. Thus of two isomeric 

 glucosides, one methyl-d-glucoside, the (a) was attacked by yeast and 

 the other (/3) only by emulsin, while the corresponding methyl-Z-glucosides 

 were not split by either of these enzymes. The corresponding glucoside 

 obtained from galactose behaves in a similar manner. 1 On the behavior 

 of amygdalin to various enzymes see page 59. In connection with 

 these observations FISCHER presents the theory that for the action of 

 an enzyme a certain correspondence in stereometric structure of the 

 enzyme and substrate must exist; the enzyme must fit the substrate 

 somewhat like a key fitting a lock. 



Then followed similar observations of DAKiN, 2 who found that racemic 

 mandelic acid ester, on incomplete hydrolysis by liver press-juice, yielded 

 a strongly dextrorotatory acid, while the ester remaining was levorotatory. 

 The dextrorotatory ester was more quickly hydrolyzed than the levoro- 

 tatory ester. Finally, we must mention the investigations of FISCHER 

 and AsDERHALDEN 3 on the cleavage of polypeptides by pancreas 

 press-juice. From abundant material they concluded that those polypep- 

 tides which consist entirely of the optical forms of amino-acids occurring 

 in nature are hydrolyzed and the others not. If in a racemic form besides 

 a polypeptide consisting of natural amino-acids, another occurs also, 

 then only the first is hydrolyzed. Besides this, other factors are also 

 of importance. Thus Z-leucyl-glycine is not hydrolyzed, although both 

 constituents occur in nature. The size of the molecule seems also to be 

 of importance, as mono-, di- and triglycyl-glycine are not split, while 

 tetraglycyl-glycine is. See also Chapter VIII. 



Retardation of Enzyme Action. There are several reasons for the 

 assumption that the hydrolytic enzymes are only active after they have 

 combined with the substrate. From this it follows that those substances 

 which prevent the formation of such combination may cause the retarda- 

 tion of enzyme action. For this reason the enzyme action is retarded 

 by such substances which adsorb the enzyme (page 49). HEDiN 4 has 

 made experiments on the retarding action of charcoal upon the action 

 of trypsin upon casein, and the action of rennin upon milk and it was 

 shown that the retardation was more pronounced if the powder and 

 enzyme were allowed to act upon each other before the substrate was 

 added than if this was present from the beginning. This fact indicates 



1 Zeitschr. f. physiol. Chem., 26, 60 (1898) (collection of Fischer's works). 



2 Journ. of Physiol., 30, 253 (1903); 32, 199 (1905). 



3 Zeitschr. f. physiol. Chem., 46, 52 (1905); 61, 264 (1907). 



*Bioch. Journ., 1, 484; 2, 81 (1906); Zeitschr. f. physiol. Chem., 50, 497 (1907); 

 60, 143 (1909). See also Jahnson-Blohm, ibid., 82, 178 (1912). 



