CHAPTER II 

 ENZYMES 



A LARGE number of the chemical changes which occur 

 in hving tissues can be imitated in the laboratory only 

 by means of high temperatures or violent reagents. With- 

 out these the changes occur at so slow a rate that they can 

 be practically regarded as not occurring at all. Such 

 reactions can, however, be brought about with great rapidity 

 in the presence of certain substances which can be prepared 

 from the hving cells. These substances, which in the 

 hving body are responsible for facilitating otherwise difficult 

 reactions, are called enzymes or ferments. Enzymes may 

 act either within or without the cell in which they are 

 produced — a distinction of no biological significance. 



Enzymes do not influence the energy changes which are 

 inherent to the reactions which they bring about. Although 

 it is possible that they act by forming compounds with the 

 substrate (as the substance upon which they act is called), 

 such compounds have but a momentary existence, the 

 enzymes appearing at the end of the reaction unaltered, 

 unless they happen to be destroyed by a secondary reaction. 

 Enzymes merely change the rate of a reaction. 



It is clear from the above description that the part played 

 by enzymes corresponds to that played by catalytic agents 

 in inorganic reactions. Enzymes may indeed be defined 

 as catalysts produced by living tissues. 



As to the chemical constitution of enzymes, little is 

 known. They are definitely not protein. They contain 

 nitrogen and probably a carbohydrate group. 



Physically, enzymes belong to the emulsoid class of 



