Table 1. Inhibition of Human Cathepsin B by Dipeptide Nitriles 1–8.

^aExperiments were performed at pH 6.0 with Cbz-Arg-Arg-pNA. Values without standard errors refer to duplicate experiments with a single inhibitor concentration of 50 μM. IC₅₀ values were calculated by using the equation IC₅₀ = [I]/(v₀/v – 1), where v and v₀ are the rates in the presence and absence of the inhibitor, respectively, and [I] is the inhibitor concentration. Values with standard errors refer to duplicate measurements with five different inhibitor concentrations. IC₅₀ values were determined by nonlinear regression using the equation v = v₀/(1 + [I]/IC₅₀). Standard error of the mean (SEM) values refer to this nonlinear regression. K_i values ± SEM were calculated from IC₅₀ values by applying the equation K_i = IC₅₀/(1 + [S]/K_m), where [S] is the substrate concentration.

^bValue was taken from ref (32).