CHAPTER 15 



EFFECTS OF VARIOUS FACTORS 

 ON INHIBITION 



The characteristics of enzyme inhibitions can usually be modified by 

 many factors and some of these changes may provide interesting information 

 on the nature of the molecular processes occurring in the interaction of the 

 enzyme with the inhibitor. We have already treated the effects of changes 

 in the concentrations of the reaction components (enzyme, substrate, acti- 

 vator, or coenzyme) and of changes in pH. Four other factors are of partic- 

 ular importance — temperature, pressure, dielectric constant, and ionic 

 strength — and this chapter will be mainly concerned with these. The re- 

 sponses of inhibition to changes in these properties of the system often make 

 it possible to determine important constants that characterize the inhi- 

 bition and give some insight into the mechanisms involved. Other means 

 may be used to alter the state of the system — as to bombard it with various 

 types of radiation, or to vary the redox equilibrium of the enzyme, or to 

 use different buffers — but these are not so apt to enlarge our knowledge 

 of the fundamental nature of the inhibitions. 



EFFECTS OF TEMPERATURE: ENZYMES 



The primary aim of investigations on the temperature dependence of 

 enzyme inhibition is the determination of certain thermodynamic quan- 

 tities, such as the enthalpy and entropy changes, associated with the for- 

 mation of the EI complex, and through these quantities to visualize more 

 accurately the energy pathway followed by the reaction. There is also a 

 practical side in certain thermal studies. The actions of insecticides that 

 are enzyme inhibitors on agriculturally important insects depend on tem- 

 perature and this aspect of the problem is a major factor in the eradication 

 of pests and their possible development of resistance to the agents. Also 

 the actions of drugs that interfere with metabolism may vary in potency 

 during states of fever or hypothermia. Very few thorough studies on the 

 variation of inhibition with temperature have been reported but enough 

 has been done in certain restricted fields to indicate the interesting results 

 that may be obtained. 



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