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 C. The activation energies for the hydrolysis of p-nitrophenyl butyrate was determined to be 11.25 kcal/mol in the temperature range of 10-37degreesC. The enzyme was unstable at temperatures higher than 50degreesC. The Michaelis constant (K-m) and V-max for p-nitrophenyl butyrate were 11 muM and 131.6 muM min(-1) mg of protein-1, respectively. The enzyme was strongly inhibited by Hg2-, Ca2+, Mg2+, Fe2+, Cu2+, Zn2+ Mn2+, Co2+, ethylemediaminetetraacetic acid (EDTA), phenylmethylsulfonyl fluoride (PMSF), and diisopropyl fluorophosphate (DFP).