An alkalophilic Bacillus sp. 103 which produced an extracellular alkaline protease, was isolated from the hemolymph of an unique Korean polychaete (Periserrula leucophryna) living in the tidal mud flats of Kwangwha island in the Korean West Sea (Yellow Sea). Maximum enzyme activity was achieved when the bacterium was grown in 2.0% soybean meal, 1% casein, 1% wheat flour, 0.5% K2HPO4,0.5% sodium citrate, 0-01% MgO4 and 0.4% sodium carbonate at 37degreesC for 48 h incubation period with agitation of 250 rpm. The enzyme has an optimum pH of around 10 and maintained its stability over a broad pH range between 5.5 and 12. The optimum temperature is around 45-50degreesC, and stability is exhibited up to 50degreesC. The alkaline protease showed extreme stability towards SDS and oxidizing agents such as hydrogen peroxide and sodium perborate, which showed activity retention of more than 90% even on treatment with 1% SDS or hydrogen peroxide for 72 h incubation. The inhibition profile exhibited by PMSF showed that the protease from Bacillus sp. 103 belongs to the family of serine proteases. (C) 2004 Elsevier Ltd. All rights reserved.