ROBERT A. ALBERTY 



activation may predominate. Effects of this type may be 

 represented by adding the following steps to mechanism (2). 



E + I , EI (17) 



E + I , IE 



IE + S , lES > IE + P 



IE + I > lEI 



Here combination of I at a neighboring site is indicated by 

 writing I to the left of E. A steady-state treatment of the 

 mechanism including these steps leads to a general equation for 

 inhibition and activation. Activation may occur if lES breaks 

 down to yield product more rapidly than does ES. 



Although a large amount of inhibition data has been ob- 

 tained and the structural features required for good inhibitors of 

 certain enzymes such as chymotrypsin are now well known (14), 

 the quantitative interpretation of inhibition constants has proved 

 to be very difficult. One complication may be that the binding 

 of inhibitor may cause appreciable shifts in ionization constants 

 of groups in the enzyme. When inhibition constants are a 

 function of pH, a comparison of the inhibition constants of a 

 series of compounds at a single pH may give erroneous indication 

 as to the actual affinities of these inhibitors for a particular 

 ionized form of the enzymatic site. Thus investigation of the 

 effects of j&H on inhibition as well as on the Michaelis constants 

 and maximum velocities would be required. 



EFFECT OF BUFFER MEDIUM 



The ideal enzyme kinetic experiment would be carried out 

 in a buffer which has no tendency to interact specifically with 

 the enzyme or substrate but which would serve simply to 

 maintain the pH and ionic environment constant while the 

 substrate concentration was varied. The need for a constant 

 pH during a series of velocity determinations is apparent from 

 the preceding section. The need for holding a constant ionic 

 environment is less obvious but equally important. Rate con- 



578 



