activity remains, even at saturating concentrations of the inhibitor, and thus
partial inhibition is observed. This partial inhibition is, in fact, analogous to
the activation phenomenon described earlier in that residual enzyme activity
exists whether effector is present at saturating levels, or not present at all.
Graphical representations discussed later, allow a simple way to visualize
whether partial inhibition is occurring. Though several types of reversible
inhibition are discussed below, regardless, proper characterization and
estimation of kinetic parameters such as the inhibition constantKiare essential
to arriving at appropriate conclusions concerning the inhibition potential of a
new chemical entity.
4.7.2 Competitive Inhibition
The most commonly observed type of enzyme inhibition is that of competitive
inhibition and it is also the simplest. As represented in Scheme 4.2, in this case
FIGURE 4.9 Eadie–Hofstee plots useful to diagnose the type of kinetics occurring
in a reaction for (a) hyperbolic (Michaelis–Menen) kinetics, (b) Sigmoidal kinetics,
(c) Biphasic kinetics with no saturation of second phase, and (d) Substrate inhibition
kinetics.
SCHEME 4.2 Competitive inhibition.102 ENZYME KINETICS