© 2006 The Japanese Biochemical Society.
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Comparison of Starch Hydrolysis Activity and Thermal Stability of Two Bacillus licheniformis 
-Amylases and Insights into Engineering -Amylase Variants Active under Acidic Conditions
1 Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502; 2 Daiwa Kasei Co., Konan-shi, Shiga 520-3203; and 3 Faculty of Bioresources, Mie University, Tsu, Mie 514-8507
* To whom all correspondence should be addressed. Tel: +81-75-753-6266, Fax: +81-75-753-6265, E-mail: inouye{at}kais.kyoto-u.ac.jp
Bacillus licheniformis 
-amylase (BLA) is widely used in various procedures of starch degradation in the food industry, and a BLA species with improved activity at higher temperature and under acidic conditions is desirable. Two BLA species, designated as PA and MA, have been isolated from the wild-type B. licheniformis strain and a mutant strain, respectively. In this study, their starch-hydrolysis activity and thermal stability were examined. MA showed higher activity than PA, especially at acidic pH (pH 5.0–5.5), and even after 1 h of treatment at 90°C. MA was active in the range of pH 4.0–8.0, which is much wider than that (pH 4.5–7.5) of PA. It was shown that the proton dissociation constants on the acidic and alkaline sides (pKa1 and pKa2) were shifted to more acidic and basic values, respectively, by the mutation of PA to MA. The activation energy and thermodynamic parameters for their thermal inactivation indicate that MA is more thermally stable and catalytically active than PA, suggesting that MA could be useful for glucose-production process coupled with reactions catalyzed by ß-amylase.
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