Determination of Kinetic Parameters for One-Substrate Reactions Under Inhibition

3 Determination of Kinetic Parameters for One-Substrate Reactions Under Inhibition 

A convenient way of expressing rate equations for reactions subjected to inhibition is in terms of apparent parameters  

For competitive inhibition Kap K and Vap = V For non-competitive inhibition Kap = K and Vap V For mixed-type inhibition there are three cases  

In mixed-type inhibition case i, the net effect will be negative irrespectively of the values of Kap and Vap. In the other two cases the net effect could be negative (inhibition) or positive (activation) depending on the values of Kap and Vap. If Kap K and Vap V the net effect will be positive (activation) irrespectively of the values of Kap and Vap. Activation by products of reaction is not as frequent as inhibition, but cases have been reported where product activation is significant (Wieloch et al. 1982 Illanes et al. 1990). 

Except for the case of uncompetitive inhibition by high substrate concentration (see Eq. 3.44), all mechanisms of inhibition can be represented by Eq. 3.45 (see, for instance, Eqs. 3.42 and 3.43) which is a very convenient expression for determining the kinetic parameters of the corresponding rate equations. 

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