Abstract: A surfactant-stable alkaline protease was isolated and purified from Bacillus licheniformis XG12, and its enzymatic properties were also characterized. A protease with high purity from strain XG12 was purified by precipitation with ammonium sulfate, DEAE-Sepharose ion exchange chromatography and Sephadex G-75 gel filtration chromatography. The purified protease exhibited a 42.6-fold enhancement in specific activity and its recovery rate was 25.3%. The enzyme was composed of a single polypeptide chain with an apparent molecular mass of 29.5 kD as determined by SDS-PAGE. This alkaline protease was highly active and stable in the pH range of 7.0－11.0 with an optimal pH of 10.0. The maximum activity of this alkaline protease was observed at 40 ℃. In addition, this protease could be activated by divalent cations such as Mg2+, Ca2+ and Mn2+ and inhibited by serine-protease inhibitors, suggesting that this alkaline protease was a serine-protease. Moreover, this alkaline protease also exhibited extreme stability towards anionic (0.1% SDS), cationic (0.1% CTAB), non-ionic surfactants (1% Tween-80, 1% Tween-20 and 1% Triton X-100) and oxidants. Due to its promising properties, this alkaline protease from Bacillus licheniformis XG12 will have potential applications in food and laundry detergents.

Key words: Bacillus licheniformis XG12, protease, purification, surfactant, characterization