Purification and properties of β-amylase from Bacillus circulans S31

A thermotolerant β-amylase was purified from Bacillus circulans S31 isolated from soil in Hong Kong. The purified enzyme has an M r of 64 kDa and was stable at 50°C and pH 7.0 for 30 min. Its K m for starch was 0.9 mg/ml with a V max of 0.3 mg/min. It was not activated by any metal ion although sulphydrys reagents were inhibitory.