• The Korean Journal of Food And Nutrition
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• v.11 no.5
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• pp.561-564
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• 1998

The stabilizatio of amaylolytic enzyme such as $\beta$-amylase of barley, $\beta$-amylase of wheat, $\beta$-amylase of sweet potato, $\alpha$-amylase of Bacillus licheniformis, $\alpha$-amylase of Aspergillus sp. and $\alpha$-glucosidase of Aspergillus awamori was attained by modification with periodate-oxidized soluble starch. The pH stability of modified enzyme was increased at pH 9 for $\beta$-amylase of sweet potato, pH 3~5 and 8~11 for $\beta$-amylase of barley, pH 2~3 and 7~12 for $\beta$-amylase of wheat and pH 6 for $\alpha$-glucosidase of Aspergillus awamori. Thermal stability increased 17.6% for $\alpha$-amylase of Aspergillus sp. at 6$0^{\circ}C$ for 10min, 30% for $\alpha$-amylase of Bacillus licheniformis at 10$0^{\circ}C$ for 5min and 4.5% for $\alpha$-amylase of sweet potato at 6$0^{\circ}C$ for 10min compared with those of native enzymes.

• Journal of Microbiology and Biotechnology
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• v.9 no.1
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• pp.62-69
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• 1999

In order to investigate the critical amino acid residues involved in the catalytic activities of $\beta$-cyclodextrin glucanotransferase ($\beta$-CGTase) excreted by Bacillus firmus var. alkalophilus, the amino acid residues in $\beta$-CGTase were modified by various site-specific amino acid modifying reagents. The cyclizing and amylolytic activities of $\beta$-CGTase were all seriously reduced after treatment with Woodward's reagent K (WRK) modifying aspartic/glutamic acid, N-bromosuccinimde (NBS) modifying tryptophan, and diethylpyrocarbonate (DEPC) modifying histidine residues. The roles of tryptophan and histidine residues in $\beta$-CGTase were further investigated by measuring the protection effect of various substrates during chemical modification, comparing protein mobility in native and affinity polyacrylamide gel electrophoresis containing soluble starch, and comparing the $K_m$ and $V_{max}$ values of native and modified enzymes. Tryptophan residues were identified as affecting substrate-binding ability rather than influencing catalytic activities. On the other hand, histidine residues influenced catalytic ability rather than substrate-binding ability, plus histidine modification had an effect on shifting the optimum pH and pH stability.