Identification of a serine protease from a Bacillus sp. using multiple loading of O'Farrell-type isoelectric focusing slab two-dimensional gel

A protease was purified from Bacillus sp. DJ isolated from Doenjang, a traditional Korean fermented food. Its molecular weight (MW) and isoelectric point (pI) were 18-19 kDa and 6.0-6.5 using 1- or 2-D fibrin zymography, respectively. The protease was optimally active at pH 9 and 55°C. Activity was inhibited by 1 mM PMSF, but not by EDTA, EGTA, aprotinin, or leupeptin, indicating that the protease is a serine protease. By using a new electrophoretic technique, multiple loading of O'Farrell-type isoelectric focusing (IEF) slab gel, the first amino acid residues of the N-terminal sequence of the protease were determined as HPLVLVDPIL, which is 80% identical with serine proteases of the subtilase family.