CHARACTERIZATION OF A THERMOSTABLE CYCLODEXTRIN GLUCANOTRANSFERASE ISOLATED FROM BACILLUS-STEAROTHERMOPHILUS ET1

A thermostable cyclodextrin glucanotransferase (CGTase) was isolated f rom 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. stearothe rmophilus strains at the nucleotide and amino acid sequence level, res pectively. The enzyme was purified to apparent homogeneity by beta-cyc lodextrin (CD) affinity chromatography and high-performance liquid chr omatography. The enzyme had an apparent molecular mass of 66,800 Da an d 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 degrees C. Thermo stability of the enzyme was enhanced by Ca2+, A 13% (w/v) cornstarch s olution was liquefied and converted to CDs solely using this enzyme. T he cornstarch conversion rate was 44% and alpha-, beta-, and gamma-CDs were produced in the ratio of 4.2:5.9:1.