3.4 Competitive and Noncompetitive Inhibition
There are 2 main types of reversible enzyme inhibition.
Competitive 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
are active.
Non-Competitive Inhibition:
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.
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