Intracellular proteases in sporulated Bacillus thuringiensis subsp. tenebrionis: detection and analysis by gelatin zymography

Three intracellular proteases were identified from sporulated cultures of Bacillus thuringiensis subsp. tenebrionis by fractionation with ammonium sulfate. In this study, we detected protease activities at Mr 92 kDa, 81 kDa and 69 kDa employing gelatin zymography. The major proteolytic activity was due to the 81 kDa protease, which was identified as a metalloprotease being inhibited by both 1,10‐phenanthroline and ethylenediamine tetraacetic acid. The proteases showed maximal azocasein hydrolytic activity at 60°C and were heat‐activated from 40°C to 60°C. The 69 kDa and 81 kDa proteases were thermo‐inactivated at 70°C and 80°C respectively, while the 92 kDa protease was still active at 80°C.