66 ENZYMES 



many other substances the reaction is very slow, and without 

 the presence of catalyzers it would go on almost or quite 

 imperceptibly. For example, ethyl butyrate saponifies on the 

 addition of water according to the following equation : 



C 2 H 5 - O - OC - C 3 H 7 + H 2 O ;j: C 2 H 6 OH + HOOC - C 3 H 7 . 



On the other hand, if ethyl alcohol and butyric acid, the prod- 

 ucts of this reaction, are placed together, they will combine to 

 form ethyl butyrate ; in other words, the reaction is reversible, 

 as indicated by the arrows in the equation. In any event, 

 however, the reaction is not complete, but continues only until 

 a certain definite proportion of ethyl alcohol, butyric acid, 

 ethyl butyrate, and water exists, when the change will stop, i. e., 

 equilibrium is established. The time that would be required for 

 this reaction to occur at room temperature would be extremely 

 long, the change being hardly noticeable, but in the presence 

 of a catalytic agent (which may be colloidal platinum or 

 lipase) the reaction goes on much more rapidly. Catalytic 

 agents, therefore, merely hasten reactions which would go on 

 without them, and they do not initiate or change the nature of 

 chemical reactions at all. When equilibrium is established, the 

 reaction stops and the enzyme has nothing more to do. Further- 

 more, and this is a recently appreciated fact, enzymes will has- 

 ten synthesis just as well as they hasten catalysis. Croft Hill 

 first showed that maltase would synthesize glucose into maltose ; 

 Kastle and Loevenhart soon after established the synthesis of 

 ethyl butyrate under the influence of lipase, and Neil son l 

 demonstrated that platinum black had the same property. 

 Taylor 2 first synthesized one of the normal body fats, triolein, 

 by the action of lipase (from the castor-oil bean) upon oleic acid 

 and glycerin. It may seem improbable at first sight that the 

 synthesis of proteids can be accomplished by enzymes, as is the 

 relatively very simple synthesis of carbohydrates and fats, but 

 the improbability disappears when we recall the well-known 

 fact that the products of proteid splitting in passage through 

 the intestinal wall disappear and are reconverted either there or 

 elsewhere into body proteids. Proteids manifestly are synthe- 

 sized and we have not a little reason to believe that this is 

 accomplished by enzymes, presumably by a reversal of their 

 action in the establishment of equilibrium. Taylor was unable 

 to synthesize protamin, one of the simplest proteids, by the 

 action of trypsin upon its cleavage products, but it has been 



1 Amer. Jour, of Physiol., 1903 (10), 191. 



2 Univ. of California Publications (Pathology), 1904 (1), 33. 



