Abstract

Extracellular protease, from Aeromonas hydrophila Ni 39, was purified 16.7-fold to electrophoretic homogeneity with an overall yield of 19.9%, through a purification procedure of acetone precipitation, and Q Sepharose and Sephacryl S-200 chromatographies. The isoelectric point of the enzyme was 6.0 and the molecular mass, as determined by Sephacryl S-200 HR chromatography, was found to be about 102 kDa. SDS/PAGE revealed that the enzyme consisted of two subunits, with molecular masses of 65.9 kDa. Under standard assay conditions, the apparent K_m value of the enzyme toward casein was 0.32 mg/ml. About 90% of the proteolytic activity remained after heating at 60 ℃ for 30 min. The highest rate of azocasein hydrolysis for the enzyme was reached at 60℃, and the optimum pH of the enzyme was 9.0. The enzyme was inhibited by the serine protease inhibitor, phenylmethylsulfonyl fluoride (PMSF), by about 87.9%, but not by E64, EDTA, pepstatin or 1,10-phenanthroline. The enzyme activity was inhibited slightly by Ca_2^+, Mg_2^+ and Zn_2^+ ions.

• Keywords: Aeromonas hydrophila; characterization; extracellular protease; purification