INHIBITIONS OF BOTH PURIFIED ENZYMES AND CELLS 883 



of the inhibition in the cells studied should be presented. Only in this 

 way can accurate and reliable correlations be made. It is important to 

 avoid, whenever possible, conclusions based on types of cells other than 

 those being investigated. 



(5) Consider the possible metabolic alteration of the inhibitor. An inhi- 

 bitor may be either changed to a more or less active substance by the 

 enzyme systems of the cells. When there occurs a significant time lag be- 

 tween the addition of the inhibitor and the effect produced, always consider 

 the possibility of a lethal synthesis. Conversely, if the inhibition decreases 

 with time, inactivation of the inhibitor may be occurring. If either occurs, 

 the time over which the inhibition is measured is verv important for the 

 interpretation of the results. 



(6) Consider the ^possible nonenzymic effects of the inhibitor. Effects on 

 cell structure and function may occur independently of any action on 

 enzymes or metabolic i^rocesses as pointed out in Chapter 9. Furthermore, 

 these effects may be brought about not only by the inhibitor itself but by 

 the other ions introduced with the inhibitor. Also the inhibitor can oc- 

 casionally alter the ionic balance in the external medium by combining 

 with one or more of the physiological ions. Such effects should, as far as 

 is possible, be distinguished from trv^e inhibition. 



(7) Localize the site of inhibition as completely as possible. The useful 

 information that may be obtained from the use of inhibitors, especially 

 new or little known inhibitors, on multienzyme or cellular systems depends 

 on how well the exact site, or sites, of inhibition can be determined, and 

 every effort to provide data for this purpose should be made. The methods 

 of localization are discussed in Chapter 11. 



(8) Exercise great care in correlating celhdar functioyi ivith an enzyme or 

 metabolic system. When cellular growth, division, secretion, movement, or 

 other functions are depressed by inhibitors, it is difficult to correlate 

 definitely these changes with a particular enzyme or metabolic sequence 

 acted upon by the inhibitor, for reasons presented in Chapter 9. One should 

 attempt to correlate with respect to inhibitor concentration, the rates of 

 inhibition, the rates of reversal of the inhibition, and the actions of sev- 

 eral similarly acting inhibitors. Evidence of specificity is especially im- 

 portant here and must be provided in some manner. 



SUGGESTIONS APPLICABLE TO INHIBITIONS 

 OF BOTH PURIFIED ENZYMES AND CELLS 



(1) Provide physiological conditions. As far as is possible, try to create 

 a normal environment for the enzyme, or mitochondria, or cells and tissues. 



