Purification and Characterization of an Alkaline Protease Produced by Alkalophilic Bacillus sp. DK1122

摘要

An alkaline protease was purified and characterized from an alkalophilic microorganism, Bacillus sp. DK1122, isolated from soil in central Korea. The optimum temperature and pH for the growth of the producer strain were 40t! and pH 9.0, respectively.The protease was produced aerobically at 40 after 24 h incubation in modified Horikoshi I medium (pH 9.0) containing 0.5% (w/v) glucose, 0.8% (w/v) yeast extract, 0.5% (w/v) polypeptone, 0.1% (w/v) K_2HP0_4, 0.02% (w/v) MgS0_4 7H_20, 1% (w/v) Na_2C0_3, and 3% (w/v) NaCl. The alkaline protease was purified by 70% ammonium sulfate precipitation of the culture supernatant of Bacillus sp. DK1122, followed by CM-Sepharose chromatography. The molecular weight of the enzyme was estimated to be 27 kDa on the basis of SDS-PAGE. The optimum temperature and pH for the protease activity were 60 and pH 9.0, respectively. Addition of CaCl_2 increased the thermal stability of the purified protease, where 90% of protease activity was retained at 60t3 for up to 3 h. Consequently, it is expected that the alkaline protease from this study, exhibiting stability at pH 7-9 and 60t!, may be promising for application in the food and detergent industries.