750 



15. EFFECTS OF VARIOUS FACTORS ON INHIBITION 



Dependence of Inhibition on Temperature 



Noncompetitive inhil)ition may vary witli the temperature because of 

 changes in either the inhibitor concentration (I) or the inhibitor constant 

 K^. The possibility of the concentration of active inhibitor being tempera- 

 ture-dependent should not be ignored. If an inhibitor exists in two or more 

 forms of unequal inhibitory potency, the equilibrium between these forms 



10 



0.8- 



2 



■4^ 



ery^ 



20' 



30' 



50' 



Fig. 15-1. Variation of noncompetitive inhibition with the temperature for var- 

 ious vfjues of AH, assuming that AH does not change with the temperature. 



Ki = 1 m.M at 37.5°. 



may be shifted by changes in the temperature. The inhibition in compet- 

 itive situations also depends on the Michaelis constant A'„, and hence on 

 the variation of this constant with tem])erature. Since K^ and K^ will 

 usually vary in the same direction with a change in temperature, due to 

 the fact that substrates and inhibitors react with the enzyme in similar 

 ways in competitive inhibition, the inhibition will generally not be so tem- 

 perature-dependent as in noncompetitive cases. However, when 7iC,„ is 

 not equivalent to K^, the change in h^ ^"'^SY cause K^,^ to vary quite dif- 

 ferently than Aj. 



