Figure 1.

A reaction scheme for an allosteric energy cycle in which an enzyme (E) can bind one substrate (A) and one allosteric effector (X). K_ia is the equilibrium dissociation constant of the substrate binding to the enzyme in the absence of effector. K_ia/x is the equilibrium dissociation constant of the substrate binding to the enzyme in the presence of saturating concentrations of effector. K_ix is the equilibrium dissociation constant of the effector when substrate is absent, while K_ix/a is the equilibrium dissociation constant of effector in the presence of saturating concentrations of substrate.