Purification and characterization of an alkaline serine protease producing angiotensin I-converting enzyme inhibitory peptide from Bacillus sp SS103

An alkaline serine protease that hydrolyzes soybean protein into strong angiotensin 1-converting enzyme inhibitory hydrolysates was isolated from alkalophilic Bacillus sp. SS103 and purified. The enzyme was purified by ammonium sulfate precipitation followed by gel filtration, cationic exchange column chromatography, and anionic exchange column chromatography. When run on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing gel, the purified enzyme gave a 36-kDa band and pI 5.5, respectively. The enzyme showed maximum activity at pH 11.0 and 50 degrees C. This enzyme activity was highly inhibited by aprotinin, suggesting it belongs to the serine protease class of enzymes. The K-m and V-max of the enzyme, when casein was used for the substrate, were 9.7 x 10(-4) mM and 244 mu g/minute, respectively. From the results of this study, it is concluded that the purified alkaline protease isolated from Bacillus sp. SS103 should be further studied for production of biofunctional hydrolysates.