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3.4 Competitive and Noncompetitive Inhibition

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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