222 THE HYDROLYZING ENZYMES 



occurs only when the forward and reverse velocities are equal, and 

 hence if the forward reaction, or reaction of hydrolysis, is accelerated 

 by a catalyzer, the reverse reaction or reaction of synthesis must also 

 be accelerated and to an exactly equal degree. If, then, the hydrolyz- 

 ing enzyme's are analogous to other catalyzers and are not consumed 

 during the progress of the reactions which they affect, they must 

 accelerate the resynthesis of the substrate from its products no less 

 than the hydrolysis of the substrate itself. 



The prediction, based upon the above premises, made by the Dutch 

 chemist Van't Hoff in 1898 that enzymatic syntheses might prove 

 possible was -verified experimentally in the same year by Croft Hill, 

 who succeeded in this manner in synthesizing a disaccharide by acting 

 upon a highly concentrated solution of glucose with the enzyme 

 Maltase obtained from yeast. 



The synthetic disaccharide was, very naturally, assumed to be 

 Maltose, but further investigation showed that the prediction of 

 Van't Hoff had not been so completely verified as was at first supposed, 

 for Emmerling in 1901 showed that the disaccharide which was actually 

 produced in Croft Hill's experiment was not maltose, or glucose-a- 

 glucoside, but a disaccharide which yields a predominating proportion 

 of /3-glucose on hydrolysis, namely glucose-/3-glucoside, or Isomaltose. 

 Now isomaltose is not hydrolyzable by maltase, so that the synthetic 

 activity of the enzyme, instead of reversing the reaction of hydrolysis, 

 produces a disaccharide which it cannot hydrolyze. It would appear 

 that a shift of equilibrium is actually occasioned by the enzyme, but as 

 there is no difference of energy-content between optical isomers, the 

 shift in the station of equilibrium caused by the enzyme is not, so far 

 as the production of isomaltose instead of maltose is concerned, of such 

 a character as to require consumption of the enzyme to accomplish the 

 liberation or absorption of energy. 



Isomaltose is, however, hydrolyzable by the enzyme Emulsin which 

 occurs in different situations from those in which maltose is found-. 

 It became at once a matter of great interest to ascertain what synthetic 

 products would result from the action of emulsin upon concentrated 

 solutions of glucose. This experiment was carried out by E. F. 

 Armstrong, who found that the product resulting from the synthetic 

 action of emulsin was not isomaltose, but Maltose. Each enzyme, 

 therefore, synthesiezs that enzyme which it cannot hydrolyze. These 

 relationships may be schematically represented by the following 

 diagram : 



Emulsin 

 Maltose < Glucose 



Glucose Isomaltose 



Maltase 



