TABLE 1

V_max values of wild-type hCE-2 and its variants toward irinotecan, p-nitrophenyl acetate, and 4-methylumberiferyl acetate Carboxylesterase activities toward the three substrates were determined as described under Materials and Methods. Concentrations used were 1 to 50 μM for irinotecan, 39 to 5000 μM for p-nitrophenyl acetate, and 62.5 to 1000 μM for 4-methylumbelliferyl acetate. V_max values were determined by three independent experiments and were expressed as mean ± S.D. Data were expressed as pmol/mg microsomal protein/min for irinotecan, and as μmol/mg microsomal protein/min for p-nitrophenyl acetate and 4-methylumbelliferyl acetate.