ENZYMES. 67 



(proteins, carbohydrates, fats). Then there also exist differences in the 

 manner in which different enzymes of the same group influence different 

 members of the same class (maltase, lactase, invertin). Finally, it is 

 possible for one enzyme to attack one of two optical antipodes and 

 the other not at all, or only to a slight degree. That optical antipodes 

 are burnt with unequal facility in the organism was shown by E. 

 FISCHER, and that of the numerous aldohexoses only three, d-dextrose, 

 d-mannose and d-galactose, and of the ketohexoses only one, d-levulose 

 are fermentable; 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 (/?) 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 FISCHER also 

 found that amygdalin, which is split into benz aldehyde, hydrocyanic 

 acid and dextrose by emulsin, is split into mandelic acid nitrile-glucoside 

 and dextrose by yeast, and from these products the first can be further 

 decomposed by emulsin into benzaldehyde, hydrocyanic acid and dex- 

 trose. 2 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, S 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 levo.ro- 

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

 FISCHER and ABDERHALDEN 4 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. 



Retardation of Enzyme Action. In the first place the products 

 of enzymotic activity have a retarding action upon the enzymes. In 



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



2 Ber. d. d. chem. Gesellsch., 28, 1508, 1896. 



3 Journ. of Physiol., 30, 253, 1903; 32, 199, 1905. 



4 Zeitschr. f. physiol. Chem., 40, 52, 1905; 51, 264, 1907. 



