CHAPTER IV 



Enzymes and Drug Action 



Functions of Enzymes 



In recent years many biologists have emphasised the 

 likelihood that a large part of the action of drugs upon 

 cells is to be explained mainly by the action of the drugs 

 on cellular enzymes. In England, for example, this was 

 particularly emphasised by A.J.Clark, R.A.Peters, 

 and D.Keilin. It may not be immediately apparent 

 vv^hy this should be so, but reasons become clear enough 

 if we consider the functions of enzyme systems in cells. 

 These functions include i. the synthesis of substances 

 which act as an immediate source of potential energy 

 for the physiological activity of the cell, e.g. the syn- 

 thesis of adenosine triphosphate; 2. the conversion of 

 potential energy to mechanical work, as is seen in mus- 

 cular contraction; 3. the protection of the cell against 

 invasion by foreign bodies — thus foreign proteins are 

 destroyed by proteases, J-amino acids by ^-amino oxi- 

 dase, hydrogen peroxide by catalase; 4. secretory ac- 

 tivity is dependent, directly or indirectly, upon enzyme 

 activity; 5. evidence has arisen, both from cytochemical 

 studies and from the study of mutations of yeasts. 



