FUNCTIONS OF DRUGS 75 



moulds and bacteria, that enzymes may be concerned 

 in the mediation of genetic effects. In fact, there are singu- 

 larly few activities of living cells in which one of the key 

 positions is not occupied by one or more enzyme systems. 



Possible Functions of Drugs in Relation 



to Enzymes 



Accepting the fact that enzymes are of vital importance 

 in the activity of cells, we must now consider the various 

 ways in which the activity of enzymes may be modified 

 by a drug. The possible modes of activity are quite 

 numerous. They include the following. 



1. Action as carriers. Substances such as methylene 

 blue and pyocyanin may act as carriers between atmos- 

 pheric oxygen and dehydrogenases: in so doing the nor- 

 mal carrier systems, such as cytochrome, are short- 

 circuited. Such an action may not at first sight appear to 

 have serious consequences. But in practice the consequen- 

 ces may be quite dramatic: for example, sea urchin eggs 

 have their respiration raised by about 200% by addition 

 of pyocyanin, and this rise is accompanied by an almost 

 complete cessation of the processes of cell division. 



2. Action as activators. Some substances are able to 

 modify the structure of an enzyme and thus modify its 

 activity. For example, reducing agents, such as b.a.l. and 

 HCN, are able to activate SH enzymes. 



3. Action as chemical inhibitors. A number of sub- 



