Physico-chemical properties of Aspergillus flavus var. columnaris alpha-amylase

The best temperature for the preservation of A. flavus var. columnaris alpha-amylase was -5 degrees C followed by 5 degrees C. CaCl2 at 0.005 M had no effect on the activity in both temperatures. Repeated freezing (-5 degrees C) and thawing followed by freezing (-5 degrees C) had no effect on stability of alpha-amylase. On the other hand, 25 degrees C was the lowest preservation temperature without any effect on the stability on alpha-amylase. 0.005 M CaCl2 decreased the activity of alpha-amylase and reached a 100% inhibition at 35th day. The fungal alpha-amylase had an optimum temperature of 55 degrees C at pH 4.6, but had 60 degrees C in buffer containing 0.005 M CaCl2 and 50 degrees C in buffer containing 0.005 M Na2-EDTA. The addition of 0.01 M CaCl2 greatly increased the thermostability of alpha-amylase at 40, 45, 50, 55 and 60 degrees C for 30 min. Optimum pH for alpha-amylase only was 5, but in the presence of 0.01 M CaCl2 or Na2-EDTA 5.6. The enzyme only was stable for 4 h at 25 degrees C. Whereas addition of 0.01 M CaCl2 showed a loss of 4% compared to a 22% loss in the presence of 0.01 M Na2-EDTA after 4 h at 25 degrees C and 65% loss in the presence of 0.01 M CaCl2 together with 0.01 M Na2-EDTA in the beginning and a 100% loss after 4 h at 25 degrees C. The optimum temperature for the activity of alpha-amylase at pH 5 was 50 degrees C for the enzyme only but 55 degrees C in the presence of 0.01 M CaCl2. However, at pH 6 and 7 optimum temperature was 55 degrees C for the activity of the enzyme only or with 0.01 M CaCl2. The presence of 0.01 M CaCl2 at pH 5, 6 and 7 resulted in increase of enzyme activity at the temperatures above 50, 40 and 25 degrees C, respectively. However, 0.01 M CaCl2 at pH 5 and 6 resulted in decreasing enzyme activity at temperatures below 55 and 45 degrees C, respectively.