EstA was purified from the supernatant by A. lwoffii 16C-1. Its molecular mass was determined to be 45 kDa, and the optimal activity occurred when the pH level was 8.0 at a temperature of 37 degrees C. The activation energies for the hydrolysis of p-nitrophenyl butyrate was determined to be 11.25 kcal/mol in the temperature range of 10-37 degrees C. The enzyme was unstable at temperatures higher than 50 degrees C. The Michaelis constant ( K(m)) and V(max) for p-nitrophenyl butyrate were 11 mocroM and 131.6 mocroM min(-1) mg of protein-1, respectively. The enzyme was strongly inhibited by Hg(2-), Ca(2+), Mg(2+), Fe(2+), Cu(2+), Zn(2+), Mn(2+), Co(2+), ethylemediaminetetraacetic acid (EDTA), phenylmethylsulfonyl fluoride (PMSF), and diisopropyl fluorophosphate (DFP).