210 Peter D. Klein 



To study the specificity independently of general reactivity, we normalize the c/s by setting their 

 sum equal to one. We consider a function called the tolerance of the apo-enzyme-substrate 

 system ; the tolerance function shall have the following properties : it shall be zero if only one 

 Ci is not zero; it shall increase with the number of substances b with non-zero c's; for a given 

 number of substances the tolerance shall be called highest if all c ,'s are equal. These postulates 

 are satisfied by the information function : 



Value of tolerance = — V ^r- log2 ^?^— 



Tentatively, one might assign a physical meaning to the tolerance as follows : the reaction 

 rates are replaced by (suitably normalized) probabilities of a reaction following a collision ; 

 it is assumed that the system can exist in a number of mutually exclusive states (configurations) 

 and that a reaction will occur if the system is in the proper configuration; then, the c^'s are 

 proportional to the fractions of the time the system is in a configuration compatible with 

 functioning with the substances 6,. The value of the tolerance is the uncertainty concerning the 

 actual state of the apo-enzyme-substrate system. 



