Purification and characterization of a H2O2-tolerant alkaline protease from Bacillus sp. ZJ1502, a newly isolated strain from fermented bean curd

•Alkaline protease was purified to homogeneity by a three-step strategy.•Enzymatic properties of the purified alkaline protease were investigated.•Kinetic constants of the purified alkaline protease were determined. Alkaline protease was purified from Bacillus sp. ZJ1502 isolated from fermented bean curd and its enzymatic properties were investigated. The final purification fold and specific activity were 18.6 and 30,230 U/mg, respectively. The molecular weight was 14 kDa by SDS-PAGE. The optimal pH and temperature were 10.0 and 40 °C, respectively. Alkaline protease showed high stability at pH 9–11. Mn2+ and Tween-80 improved its activity by 22% and 31%, respectively, while SDS, CMC and EDTA respectively inhibited its activity by 33%, 47% and 22%. Alkaline protease exhibited poor tolerance to n-butyl alcohol and ethanol, but showed resistance to H2O2. 29.8% of the original activity was still retained after 0.5 M H2O2 treatment for 3 min. The Km and Vmax values of this enzyme towards casein were 16.7 mg/ml and 14.7 µg/(min·ml), respectively. This study provides a basis for understanding enzymatic properties of Bacillus sp. ZJ1502 alkaline protease.