TWO INHIBITORS ACTING ON A SINGLE ENZYME 



497 



These equations are plotted for different values of a in Fio. 10-4. The 

 general shapes of the curves are seen to be independent of the type of inhi- 

 bition involved; e.g.. when the inhiliitors prevent each other's Innding 



Fig. 10-4. Isobologram for two inhibitors acting on a single en- 

 zyme (see Eqs. 10-17 to 10-19). K^ = 3 mM, A',^ = 0.5 mM, 

 Ki = 2 mM, (S) = 5 mM, and i = 0.5. Both competitive: curve 

 1, a — 00; cm've 2, a = 1; curve 3, a = 0.3. Both noncompe- 

 titive: curve 4, or = oo; curve 5, a = 1; curve 6, « = 0.3. Ii 

 competitive and I, noncompetitive: curve 7, a = cO; curve 8, 

 a = 1; curve 9, c< = 0.3. 



{a = go), the isobols are linear (curves 1, 4. and 7) in all cases. As the in- 

 hibitors interfere less and less with each other (cc decreasing), the curves 

 become progressively more concave upwards. 



