A thermostable cyclodextrin glucanotransferase (CGTase) was isolated
from a Bacillus stearothermophilus strain, ET1, which was screened from Korean soil. The
corresponding CGTase gene cloned
in Escherichia coli shared 84% and 88% identity with
CGTase genes from other B. stearothermophilus
strains at the nucleotide and amino acid sequence level, respectively.
The enzyme was purified to
apparent homogeneity by β-cyclodextrin (CD) affinity chromatography
and high-performance liquid
chromatography. The enzyme had an apparent molecular mass of
66,800 Da and a pI of 5.0. The
optimum pH for the enzyme-catalyzed reaction was pH 6.0, and the
optimum temperature was
observed at 80 °C. Thermostability of the enzyme was enhanced by
Ca2+. A 13% (w/v) cornstarch
solution was liquefied and converted to CDs solely using this enzyme.
The cornstarch conversion
rate was 44% and α-, β-, and γ-CDs were produced in the ratio of
4.2:5.9:1.
Keywords: Cyclodextrin glucanotransferase; thermostability; cyclodextrin;
Bacillus stearothermophilus
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