RATES OF INHIBITION OF PURE ENZYMES 



551 



comparable to the inhibitor concentration. In mutual depletion systems, 

 the logarithmic plots of the remaining activity against time deviate from 

 straight lines in a manner shown in Fig. 12-15. Such curvatures are fre- 

 quently seen in plotting experimental data and in certain cases may be 

 due to the factor of inhibitor depletion. It must be remembered that in 

 enzyme preparations containing nonenzymic material capable of binding 

 the inhibitor, depletion of the inhibitor will occur more readily than in pure 

 enzvme solutions and this can give rise to deviations of this type. 



TIME 



MIN 



Fig. 12-14. Effect of the enzyme concentration on the rate of inhibition in a mutual 

 depletion system (Eq. 12-24). (I«) = 1 mJ/ and k^ = 100 min-i. Curve 1, (E«) = 

 0.01 m2I; ciu've 2. (E^) = 0.1 mJ/; curve 3, (E«) = 0.5 mM; curve 4, (E^) = 1.6 mM; 



curve 5, (E^) = 2 mM. 



An irreversible inhibition has been discussed because the kinetics of 

 a reversible mutual depletion system, E + I ^ EI, are rather complex. 

 The rate equations: 



f/(EI) 

 dt 



= A-/(E,) - (EI)] [{],) - (El)] - A-_, (El) 



(12-25) 



di 

 dt 



- A-,(l,) - ik,[(E,) + (h) + K,] + iH-AE,) 



(12-26) 



