94 ENZYMES AND DRUG ACTION 



or more enzyme systems is in fact the result of a parti- 

 cular enzyme poison. 



Biological Aspects of Enzyme Studies 



When we look at the results of enzyme studies from the 

 point of view of a biologist, we find a number of difficul- 

 ties in applying these studies to cellular systems. These 

 are: 



1 . Among the characteristic activities of many cells is the 

 capability of concentrating foreign substances in va- 

 cuoles or granules. The biochemist is accustomed to 

 adding a certain amount of enzyme poison to his en- 

 zyme solution or suspension, and then considering 

 that the poison is uniformly distributed in the mate- 

 rial under observation. But there is no such uniform 

 distribution likely to occur in cellular systems, and 

 the calculation of average concentrations for cellular 

 systems is often fruitless, and even misleading. As a 

 result of the concentration of drugs in particular lo- 

 calities in cells, a drug may never come into contact 

 with the cellular systems which in vitro are the most 

 sensitive to it. 



2. Up to now the enzymes which have been mostly stud- 

 ied by biochemists have been cytoplasmic systems. 

 It is much more difficult to make adequate studies on 

 the enzymes of nuclei. Yet substances acting in very 

 low concentrations are at least as likely to exercise 



