3.4 Competitive and Noncompetitive Inhibition
There are 2 main types of reversible enzyme inhibition.
The inhibitor binds to the active site and
competes with the substrate for binding. In this case, at low [S], the
inhibitor competes for the active site and effectively lowers the [S] at the
active site. This lowers the rate at low [S]. This increases the apparent
Km. At very high [S], the level of S overcomes the inhibition by mass action
and Vo approaches Vmax. Vmax is unchanged because all of the enzyme molecules
The inhibitor binds to another site on the enzyme and inactivates the
enzyme molecule. This effectively reduces the [E]tot available for
catalysis. Since Vmax is proportional to [E]tot, Vmax is reduced. Since
the remaining active enzyme molecules are unaltered, Km is unchanged.
The next page illustrates solving kinetics problems.