870 



16. SPECIFICITY OF INHIBITION 



modification of the structure, as well as react with coenzymes or cofactors. 

 With respect to the enzymes themselves, the specificity in systems contain- 

 ing three or more enzymes may be treated by an extension of the formu- 

 lation given in the preceding section. The over-all specificity may be de- 

 signated by a series of individual specificities: 0^2 = h — h^ ^^la — h ~ h^ 

 etc. A situation such as shown in Fig. 16-4 might occur, in which five differ- 

 ent enzymes are inhibited to varying degrees by an inhibitor. The problem 

 arises as to the optimal inhibitor concentration to use. This cannot be 

 decided by simply inspecting a diagram of this type, because consideration 

 must also be given to the importance of the various enzymes in what is 



Fig. 16-4. Inhibition-concentration curves for a system 



of hypothetical enzymes, Ej to E5. See the text for 



explanation. 



being measured. The concentration (1)2 will give the maximal specificity 

 for inhibitions of E^ and Eg and if Eg is an important enzyme in the study, 

 inhibitor concentrations above this cannot be readily used; however, if 

 E2 can be neglected due to its obvious nonparticipation in the system being 

 investigated, the specificity at this concentration will increase. If both 

 E2 and E3 may be neglected, inhibitor concentrations up to (1)3 may be 

 used, which gives the maximal specificity for inhibition on E^ and E4. 

 If the role of the enzymes in the process beng measured in unknown, a 

 concentration around (I)i might well be used for the most certain interpre- 

 tation of the data. Lastly, if the concentration (1)4 had been used arbitrarily, 

 or simply because it completely inhibited E^, one can see that Eg and E3 

 would also be strongly inhibited, while E4 would be partially inhibited, 

 so that no clear interpretation would be possible. Actually, it would appear 

 that such high concentrations are frequently used in complex systems and 



