The effect of sodium chloride on the serine-type fibrinolytic enzymes and thermostability of extracellular protease from Bacillus amyloliquefaciens DJ-4

Abstract

By adding sodium chloride (2.5%) into a Bacillus amyloliquefaciens DJ-4 culture broth, two serine-type fibrinolytic proteases with a molecular weight of 29 (subtilisin DJ-4) and 38-kDa were stimulated on the SDS-fibrin zymogram or inhibitor gels. B. amyloliquefaciens DJ-4 showed the highest proteolytic activity (5.52 plasmin NIH unit/ml) on the fibrin plate based on the molar ratio when cells were subjected to the 2.5% NaCl. Using a fibrin plate, the secreted protease from this strain in the presence of 5% NaCl showed that about 49% of the enzyme's activity remained after incubation at 60°C for 30 min, but as the salt concentration was increased (10% NaCl) the activity nearly disappeared (0.14 plasmin NIH unit/ml). However, through a fibrin zymography assay, three fibrinolytic enzymes (38,53 and 80-kDa) from the cells in the presence of 10% NaCl were detected. Also, two salt-activated serine-type fibrinolytic proteases (29 and 38-kDa) showed thermostability from 65 to 70°C for 30 min. Furthermore, these proteases also showed stability, pH 6-11. In particular, 29-kDa (subtilisin DJ-4) was very stable in the pH range of 4-11 at 4°C for 48 h.