Production of a thermophilic, extracellular alkaline protease by Bacillus stearothermophilus AP-4.

A thermophilic Bacillus stearothermophilus strain AP-4 excreting a thermostable alkaline protease, was isolated from a local compost. Maximum activity of protease (250 U/ml) was after 36 h growth in broth at pH 9.0 and at 55°C. The protease was optimally active at pH 9.0 and 55°C and was stable in 5 mM CaCl2. The enzyme was completely inactivated by PMSF, EDTA and β-mercaptoethanol. It is therefore a metal ion-dependent, alkaline, serine protease.