ENZYME INHIBITION AND CHANGES IN CELL FUNCTION 



465 



vidua! metabolic pathways. If a cell performs three functions — F^, F^, 

 and F^ — the energy required for the normal maintenance of each function 

 will be £"1, E2, and E^. Assuming, for simplicity, that these make up the 

 total cell activity, the energy requirement for the cell is E^ = E^ ^ E2 + 

 E^. The energy-supplying reactions provide energy equivalent or in excess 

 of this, but in the i^resence of an inhibitor the energy supph' may drop 

 below E, as illustrated in Fig. 9-6. If the inhibition lowers the energy pro- 



ENERGY 

 SUPPLY 



ENERGY 

 REQUIREMENT 



Fig. 9-6. Relationship between meta- 

 bolic energy supply and functional 

 energy requirement. The heights of 

 the solid bars represent the energy 

 requirements for the three different 

 functions and E^ is the total require- 

 ment. The normal energy supply is E^ 

 and the reductions by inhibition are 

 indicated by the numbers. See text for 

 detailed explanation. 



duction to level 1, it is possible that all the functions will be depressed 

 somewhat, or, if one function has preference over the others (that is, if a 

 function is able to obtain the energy available more efficiently), it will 

 remain unchanged at the expense of the others. But when the energy supply 

 is lowered to level 2, it is evident that F-^ could not continue normally, 

 although F^ and F^ may still do so. At level 3, only i^g could remain normal 

 and then only if it had preference. In such cases the results may be thought 



