Extracellular thermostable alpha-amylase from Bacillus stearothermophilus Q8

The alpha-amylase of Bacillus stearothermophilus Q8, previously isolated in our laboratory, was purified by ammonium sulfate precipitation and CM-sephadex chromatography. The activity the of partial purified alpha-amylase was to be protected by bovine serum albumin Ca2+ and Mg2+. The enzyme showed 100% activity at pH 9.0; 98%, at pH 8.0 and 41%; at pH 10.0. It expressed optimal reaction temperature at 90 degrees C, 81% of the activities remained at 100 degrees C. After 15 min incubation at 100 degrees C with the addition of 10 mM Ca2+, the enzyme only retained 67% activity. The enzyme, however, retained 10% of the maximal activity after 2 h incubation at 90 degrees C, in the absence of substrate and with the addition of Ca2+. Of cations, Na+ at 0.1 and 1 mM, Mn2+ at 0.1 mM showed stimulatory effect; of anions OH-Cl-I-HCO3-NO2-N3- at 10 mM showed stimulatory effect. Addition of urea and KMnO4 resulted in the loss of enzyme activities; however, lower concentration of SDS and Tween 80 afforded protection of the enzyme activities. Galactose and maltose were non-inhibitory for the enzyme activities, while, fructose, mannose, xylose and lactose were slightly inhibitory. The relative hydrolysis sequence of polysaccharides were amylose greater than soluble starch = corn starch greater than glycogen.