2 1. PERSPECTIVES OF METABOLIC INHIBITION 



on an intricate structure, the possibility of life depending upon a proper and 

 accurate coordination of the rates of these various processes. The intro- 

 duction of an inhibitor into the system leads to an alteration of certain 

 rates and a disturbance of this balance. The extent to which the imbalance 

 will affect the total system will depend upon many factors. One can usually 

 measure only the results of the imbalance and, hence, must always be aware 

 of the factors that stand between the metabolic dislocation and what is 

 measured. If the inhibitor shifts the balance to the detriment of the organ- 

 ism, it is generally classed as a poison; when the balance is shifted in favor 

 of the survival of the total system, the inhibitor may be considered as a 

 drug. 



The actions of inhibitors upon living systems can often be most profitably 

 visualized by interpreting the results in terms of a modification of the energy 

 flow (Fig. 1-1). There are many ways of deviating the course of the flow 



SUBSTRATES 



EAT 



PRODUCTS 



Fig. 1-1. Scheme of the basic energy 

 flow through a celL 



of energy through cells and, therefore, in some manner altering the bio- 

 chemical morphology and the functional phenomena necessary for the life 

 of the cell and for the cell's role in the life of the total organism. The prin- 

 cipal pathways of energy flow are indicated in the diagram and it is possible 

 in this scheme to designate some of the general loci at which inhibitors may 

 act. An inhibitor may interfere with the entrance of the substrates into the 

 cell (1) by altering permeability or depressing transport mechanisms; in 

 this way the inhibitor can reduce the total potential energy available to 

 the cell. The action may also be exerted on any of the metabolic pathways 

 whereby energy and matter are distributed, especially on the degradative 

 reactions in which the substrates are broken down oxidatively to products 



