THE NATURE OF ENZYME ACTION 21 



It was found that this enzyme, acting on the optically inactive 

 mandelic esters, hydrolysed more rapidly the dextro component 

 than the laevo one. In this way the percentage of dextro- 

 mandelic acid in the products of the reaction was greater at first 

 than that of the laevo-mandelic acid ; as the reaction proceeded 

 the relative amounts became closer, until finally both were 

 present in equal quantity and the acid was optically inactive. 

 These facts can only be satisfactorily explained on the hypo- 

 thesis that the enzyme is itself optically active and forms 

 addition compounds with the ester. In the words of Dakin, 

 "The dextro and laevo components of the inactive ester first 

 combine with the enzyme, but the latter is assumed to be an 

 optically active asymmetric substance, so that the rates of 

 combination of the enzyme with the d. and 1. esters are different. 

 The second stage in the reaction consists in the hydrolysis of 

 the complex molecules of (enzyme + ester). Since the complex 

 molecule (enzyme -f d. ester) would not be the optical opposite 

 of (enzyme + 1. ester), the rate of change in the two cases would 

 again be different. Judging by analogy with other reactions one 

 might anticipate that the complex molecule which is formed with 

 the greater velocity would be more rapidly decomposed. In the 

 present case it would appear that the dextro component of the 

 inactive mandelic ester combines more readily than the laevo 

 component with the enzyme, and that the complex molecules 

 (d. ester 4- enzyme) are hydrolysed more rapidly than (1. ester + 

 enzyme), so that if the hydrolysis be incomplete dextro acid is 

 found in solution and the residual ester is laevo-rotatory." 



We have as yet no definite information as to what happens 

 after the combination between enzyme and substrate has taken 

 place. In the case of inorganic catalysts the most acceptable 

 explanation is that the intermediate compound is split up again 

 with the formation of the particular products of the reaction and 

 the liberation of the catalyst in its original form. The intermediate 

 formation of ethyl-sulphuric acid in the production of ether and 

 that of nitrosyl-sulphuric acid in the old chamber process of 

 manufacture of sulphuric acid may be given as illustrations. 

 Practical experience has found that in the latter process the 

 nitric acid gradually disappears in the form of bye-products, so 

 that the catalyst is not completely restored. This fact is of 

 importance in connection with the view taken by some investi- 

 gators that certain bodies, such as Buchner's zymase, are not 



