A steady state mathematical model for stepwise “slow-binding” reversible enzyme inhibition

The standard mathematical model for stepwise “slow-binding” enzyme inhibition (E+I⇌EI⇌EI∗)(E+I⇌EI⇌EI∗) assumes that the initial enzyme–inhibitor complex EIEI is always at equilibrium with the free component species EE and II. This assumption implies that the dissociation rate constant (EI→E+I)(EI→E+I) is infinitely higher than the isomerization rate constant for EI→EI∗EI→EI∗. This paper presents a more general mathematical treatment, under the steady state approximation rather than the usual rapid-equilibrium approximation, whereby the two rate constants for the disappearance of EIEI are allowed to be comparable in magnitude. Experimentally relevant illustrative examples include discrimination between a single-step and a two-step mechanism for slow-binding inhibition kinetics.