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The a-amylase from Bacillus licheniformis was purified and its thermostability in the presence of substrate and metal was ions investigated. Comparing D-values of the enzyme obtained in the presence of Ca^(++), g^(+++) and both CaT^(++) and B^(++) ions, the thermostability of the enzyme was markedly enhanced by the addition of metal ions. Ca^(++) and B^(+++) ions exhibited a protective action, the former ion being more effective, and both ions showed a synergistic effect. The enthalpy of activation for the thermal inactivation in the presence of metal ion was 320.2 kJ/mole for Ca^(2+) ion, 212.9 kJ/mole for B^(+++), while it was 183.9kJ/mole in the absence of metal ions. In the thermal inactivation for 30 min at 96℃ , the residual activity in the presence of 30% (w/w) starch was 51.0%, whereas the presence of Ca^(++) ion additionally provided a remarkable thermo-resistance.
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