Competitive enzyme
In competitive inhibition, at any given moment, the enzyme may be bound to the inhibitor, the substrate, or neither, but it cannot bind both at the same time. In viually every case, competitive inhibitors bind in the same binding site as the substrate, but same-site binding is not a requirement. A competitive inhibitor could bind to an allosteric site of the free enzyme and prevent substrate binding, as long as it does not bind to the allosteric site when the substrate is bound. For example, strychnine acts as an allosteric inhibitor of the glycine receptor in the mammalian spinal cord and brain stem. Glycine is a major post-synaptic inhibitory neurotransmitter with a specific receptor site. Strychnine binds to an alternate site that reduces the affinity of the glycine receptor for glycine, resulting in convulsions due to lessened inhibition by the glycine. In competitive inhibition, the maximum velocityof the reaction is unchanged, while the apparent affinity of the substrate to the binding site is decreased the dissociation constant is apparently increased). The change in K m (Michaelis-Menten constant) is parallel to the alteration in K d . Any given competitive inhibitor concentration can be overcome by increasing the substrate concentration in which case the substrate will outcompete the inhibitor in binding to the enzyme.
Increase Km and Vmax no change
Km decrease, Vmax increase
Km and Vmax both decrease
Km and Vmax both increase
Enzymes