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Bacillus amyloliquefaciens α - amylase 의 구조적 안정성에 대한 분광학적 및 전기영동 연구
오화섭,김광희,서세원,최명언 ( Hwa Seop Oh,Kwang Hee Kim,Se Won Suh,Myung Un Choi ) 생화학분자생물학회 1991 BMB Reports Vol.24 No.2
The nature of calcium ion binding to α-amylase from Bacillus amyloliquefaciens was examined to investigate its effect on the structural stability of the enzyme. Calcium ion provided an excellent protection against the destruction of the enzyme activity by heat, protease, and denaturing agents. The structural change of α-amylase upon binding of Ca^(2+) has been studied by circular dichroism, fluorescence, and UV difference absorption spectroscopy. Upon binding calcium ions, the content of α-helical structure of α-amylase increased significantly and the binding constant of calcium to α-amylase was found to be about 4.8 mM at pH 7.5. The fluorescence emission spectrum showed that the calcium-free enzyme had different λ_(max) from the native enzyme. The λ_(max) of the Ca^(2+)-free enzyme shifted to longer wavelength by 15 nm and the intensity at λ_(max) decreased compared to the native enzyme. Furthermore, the protective nature of calcium ion binding was examined by electrophoretic techniques. The fragmentation pattern of α-amylase following an irreversible thermoinactivation at 90℃ was analyzed by SDS-PAGE. The native and calcium-free enzymes showed a marked difference in the electrophoretic patterns. In the case of native enzyme, the aggregate of the main band (54.7 kD) appeared gradually as high-molecular mass traces on the top region of the gel. However, in the case of Ca^(2+)-free enzyme, the main band disappeared rapidly and new distinct bands of smaller molecular masses (40.2 kD, 22.0 kD, 13.1 kD) appeared. The digestion patterns of α-amylase by trypsin were also different between the native and Ca^(2+)-free enzyme. From these results it can be concluded that the binding of Cat` ion contributes markedly to the structural stability of α-amylase.
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