Thermostable alkaline protease produced by Bacillus thermoruber, a new species of Bacillus

• The proteolytic activity produced by a new species of Bacillus isolated in our laboratory was investigated. This enzyme was purified to homogeneity from cell-free culture liquids of B. thermoruber. The purification procedure included ion-exchange chromatography on DEAE-Sephadex A-50 and -casein agarose affinity chromatography. The protease consists of one polypeptide chain with a molecular weight of 39000±800. the isoelectric point was 5.3; the optimum pH and temperature for proteolytic activity (on casein) was found to be pH 9 and 45°C respectively. Enzyme activity was inhibited by PMSF and EDTA. The stability was considerably increased by addition of Ca2+, and the protease exhibited a relatively high thermal stability. The alkaline protease shows a preference for leucine in the carboxylic side of the peptide bond of the substrate. The K m value for benzyloxycarbonyl-Ala-Ala-Leu-p-nitroanilide was 2.5 mM.