IC₅₀ values and inhibition constants (K_i) of prostaglandin inhibitors.

aEnzyme activity in the presence of prostaglandin inhibitors was determined at pH 7.5 and 25°C, with 1 mM CDNB and 1 mM GSH and 4% (v/v) DMSO. The mean percent inhibition from five affinity-purified GST concentrates was used to calculate IC50 values. bKi values were calculated using the Cheng-Prusoff equation with an Km value of 0.41 mM for CDNB obtained from the average of two independent experiments; a CDNB substrate concentration of 1 mM; and IC50 values listed in the table above. cIn an attempt to constrain the likely range of calculated Ki values, test calculations using Km values for CDNB ranging from 0.1 mM to 1.0 mM resulted in Ki values for 15(S)-PGA2 of 6.0 to 37.7 µM.