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Chemistry · Glossary

What is Inhibition?

Also known as: competitive inhibition · inhibition constant · uncompetitive inhibition · mixed inhibition

Definition 13.14 University Chemistry — Year 3 · Chapter 13 — Complex Kinetics: Chains, Enzymes and Oscillations

An inhibitor I binds the enzyme reversibly. In competitive inhibition it binds only the free enzyme, at the active site, with the inhibition constant KiK_i (dissociation constant of EI); in uncompetitive inhibition it binds only ES, with the constant Ki′K_i'; in mixed inhibition it binds both.

Michaelis–Menten kinetics with K_M = 0.80\, mM and V_ = 0.50\, µ M\, s-1 (model): no inhibitor (black), a competitive inhibitor at [ I] = 2K_i (blue, K_M tripled, same V_) and an uncompetitive one at [ I] = K_i' (red, K_M and V_ halved). Right: the Lineweaver–Burk lines; the competitive line meets the uninhibited one on the 1/v axis, the uncompetitive one is parallel to it (1/[ S] in mM-1, 1/v in s\, µ M-1).
Michaelis–Menten kinetics with KM=0.80 mMK_M = 0.80\,\mathrm{mM} and Vmax⁡=0.50 µM s−1V_{\max} = 0.50\,\text{µ}\mathrm{M}\,\mathrm{s}^{-1} (model): no inhibitor (black), a competitive inhibitor at [I]=2Ki[\mathrm I] = 2K_i (blue, KMK_M tripled, same Vmax⁡V_{\max}) and an uncompetitive one at [I]=Ki′[\mathrm I] = K_i' (red, KMK_M and Vmax⁡V_{\max} halved). Right: the Lineweaver–Burk lines; the competitive line meets the uninhibited one on the 1/v1/v axis, the uncompetitive one is parallel to it (1/[S]1/[\mathrm S] in mM−1\mathrm{mM}^{-1}, 1/v1/v in s µM−1\mathrm{s}\,\text{µ}\mathrm{M}^{-1}).
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