O PHYSIOLOGICAL CHEMISTRY. 



is unknown. The co-enzyme action, in this case, is probably de- 

 pendent upon the presence of two individual agencies, one of which 

 is phosphates. 



It has been shown by Loevenhart that the property of acting 

 as a pancreatic lipase co-enzyme is vested in bile salts, and Magnus 

 has further shown that the synthetic salts are as efficient in this 

 regard as the natural ones. A few other instances of co-enzyme 

 demonstrations have been reported. 



The so-called " specificity " of enzyme action is an interesting 

 and important fact. That enzymes are very specific as to the 

 character of the substrate or substance acted upon, is well known. 

 Emil Fischer investigated this problem of specificity extensively 

 in connection with the fermentation of sugars and reached the 

 conclusion that enzymes, with the possible exception of certain oxi- 

 dases, can act only upon such substances as have a specific stereo- 

 isomeric relationship to themselves. He considers that the enzyme 

 and its substrate must have an interrelation, such as the key has 

 to the lock, or the reaction does not occur. Fischer was able to 

 predict, in certain definite cases, from a knowledge of the consti- 

 tition and stereo-chemical relationships of a substance, whether 

 or not it would be acted upon by a certain enzyme. An applica- 

 tion of this specificity of enzyme action may be seen in the well- 

 known facts that certain enzymes act on carbohydrates, others on 

 fats, and others on protein, and moreover, that the group of those 

 which transform carbohydrates, for example, is further subdivided 

 into specific enzymes each of which has the power of acting alone 

 upon some one sugar. 



It has been conclusively shown, in the case of certain enzymes, 1 

 at least, that their action is a reversible one and is, in all its main 

 features, directly analogous to the reversible reactions produced by 

 chemical means. For instance, in the saponification of ethyl-buty- 

 rate by means of pancreatic lipase, it has been shown that upon the 

 formation of the end-products of the reaction, i. e. } butyric acid 

 and ethyl alcohol, there is reversion 2 and the reaction is stationary. 

 This does not mean that there are no chemical changes going on, 

 but simply indicates that chemical equilibrium has been established, 



1 This is probably a general condition. 



2 The re-synthesis of ethyl-butyrate from its hydrolysis products. This may be 

 indicated thus : 



C 3 H 7 COO-C 2 H 3 + H 2 O ?=* CsHzCOOH + C 2 H 5 OH. 



Ethyl but yratc. Butyric acid. Ethyl alcohol. 



