| Abstract: | 1,4-α-D -glucan maltohydrolase (β-amylase, EC.3.2.1.2.) produced by Bacillus polymyxa was isolated and purified. Some of its properties were examined and compared with those of a typical plant β-amylase. Hydrolysis of periodate oxidised amylose demonstrated an exo mechanism of substrate attack similar to that of sweet potato β-amylase. The effect of sulphydryl reagents on enzyme activity was similar to that reported for plant β-amylases. Consistent with the observation that the enzyme has an exo mechanism of action, it also failed to degrade Schardinger cyclodextrins. These latter compounds acted as inhibitors of the enzyme. The optimum temperature for activity was 37 °C. The enzyme was quite stable at temperatures up to and including 37 °C; 90% of the original activity remained after storage at 37 °C for 6 days. However, the stability decreased rapidly when exposed to temperatures above 37 °C; only 20% of the activity remained after 1 h at 45 °C. The hydrolase exhibited a rather sharp optimum at pH 6.8 for stability at 37 °C. However, the enzyme was quite stable in the pH range 6.4–7.2 at 20 °C but it was shown to be less stable in acidic conditions than the corresponding plant enzymes. |
