Table 2

Effects of various chemicals on phenacetin deacetylase activity in human liver microsomes

ChemicalConcentration Range TestedMaximum Inhibition or (Stimulation)
mM %
Ester-type compound
 Acetylsalicylic acid0.1–106.8
 Clofibrate0.1(0.6)
 Dilazep0.138.1
p-Nitrophenylacetate0.1–109.2
p-Nitrophenylpropionate0.1–108.1
 Oxybutynin0.1–0.530.6
 Procaine0.1–125.8
Amide-type compound
 Acetanilide0.1–1027.7
O-Acetamidophenol0.1–1020.2
p-Acetamidophenol0.1–1018.1
 Aniracetam0.1–17.1
 Captopril0.1–100.5
 Flutamide0.001–0.2(349)2-a
 Phenobarbital0.1–1034.5
 Prazosin0.0003–0.326.6 μM (IC50)2-b
 Procainamide0.1–1026.7
Other compound
 BNPP0.01–1096.32-c
 PMSF0.01–132.72-c

Phenacetin (2.5 mM) and each chemical were coincubated with 4 mg/ml microsomal protein in the assay buffer (pH 8.6) at 37°C for 30 min. Enzyme incubation and metabolite analysis were carried out in duplicate, and the data were expressed as the mean. Control activities were 1.73 to 2.04 nmol/min/mg of protein.

  • 2-a The value of the maximum stimulation by flutamide was estimated from the data presented in Fig. 4.

  • 2-b The IC50 value for prazosin inhibition was calculated from the data presented in Fig. 2.

  • 2-c The inhibitory profiles of phenacetin deacetylation for BNPP and PMSF are presented in Fig. 3.