Module 12: Figure uncompetitive inhibition
Different types of inhibitory action.
Inhibitors can act in different ways. In competitive inhibition, they compete with a substrate for the same binding site. In non-competitive inhibition, the inhibitor binds to a separate site to induce a conformational change that inhibits the substrate-binding site. Finally, there is uncompetitive inhibition, where the binding site for the inhibitor appears only when the substrate is bound. This uncompetitive mechanism, which is the way that Li+ works, introduces a usage-dependent aspect to the inhibition. At low substrate concentrations, there will be little enzyme–substrate interaction and there will be little inhibition by Li+, but as the substrate concentration increases, there will be a corresponding and progressive increase in its inhibitory action.