It should be noted that under tight-binding experimental conditions k obs vs. [I] 0 plots derived from the classical rate equation Eqn (1) are often very similar to k obs vs. [I] 0 plots derived from Eqn (4). Thus, many enzymologists involved in drug-discovery research may have encountered nearly linear k obs plots that (i) do not go through origin but instead intersect the Y-axis below the zero point; and (ii) are concave upward, or even show a distinct minimum, at low inhibitor concentrations instead of appearing either linear or hyperbolic (concave downward). As we can see from Figure , both of these qualitative characteristics are clear hallmarks of tight-binding (inhibitor depletion) actually occurring in the assay.