N-acetyltransferase from Aeromonas hydrophilia was purified by ultrafiltration, DEAE-Sephacel, eel filtration chromatography on Sephadex G-100, and DEAE-5pw on high performance liquid chromatography, as judged by sodium dodecyl sulfate-polyacrylamine gel electrophoresis (SDS-PAGE) on a 12.% (wt/vol) slab gel. The enzyme had a molecular mass 44.9 kDa. The purified enzyme was thermostable at 37 degrees C for 1 h with a half-life 28 min at 37 degrees C, and displayed optimum activity at 37 degrees C and pH 7.0. The K-m and V-max values for 2-aminofluorene were determined to be 0.896 mM and 2.456 nmol/min/mg protein, respectively. Among a series of divalent cations and salts, Zn2+, Ca2+, and Fe2+ were demonstrated to be the most potent inhibitors.