KINETICS OF COMPLEX ENZYME REACTION TYPES 



41 



When a ternary EAB complex is formed, in which B is not necessarily 

 attached to the enzyme, one can wi-ite: 



E + A ^ EA 



EA + B ^ EAB -^ EC - D 



k_. 



EC ^ E + C 



(2-55) 

 (2-56) 



(2-57) 



and the rate equation is the same as Eq. 2-54 with V,„ = k.2k3{Yij)!{k_2- 

 K' = ^2^3/^1(^-2+^3)' and K" = k2{k3-\-k,)lk,{k_2+h). 



It is obvious that these three mechanisms cannot be distinguished by 

 the usual kinetic analysis and although it is often possible to evaluate the 

 general constants, one is seldom able to interpret them in terms of rate 

 constants or demonstrate a particular mechanism with certainty. 



(b) Both Substrates Form Complexes With The Enzyme. The most 

 general situation is where both substrates can form separate complexes 

 with the enzyme and a ternary EAB complex is formed by either order 

 of addition of the substrates: 



EA 



EAB 



E + C + D 



(2-58) 



The steady-state treatment leads to a complex rate expression with nu- 

 merous constants, each a function of several rate constants, which is not 

 of the Michaelis-Menten form and does not give a linear reciprocal plot: 



V = 



(A) ^""^ (B) +''' (B) 



K, +^ ^A%(A)-^A'io(B)^/C„-— -- 



8 ^_^^ 9V (A)(B) 



(2-59) 



where the constants have the following values: 



Ki = kik^skik^i^Eit) -t- k.iksktk-^iFit) 

 K, = kM-ok.CEt) 

 K3 = kskikik^iYif) 



