Bombyx mori and Philosamia cynthia ricini silk fibroins were employed for preparing enzyme membranes. Glucose oxidase (GOD) was entrapped in the silk fibroin membrane without glutaraldehyde treatment. The entrapped GOD was tested with the colorimetric method. The activity yield of GOD was 98.7% when 3.71 × 10-3 U of GOD were immobilized in 1.1 mg dry weight B. mori silk fibroin membrane (300 μm). The enzyme leakage from the enzyme membrane was only 0.05% after 36 days. In addition, the activity after heating at 60°C for 20 min was unchanged. IR spectra indicated that the GOD-B. mori silk fibroin membrane contained 80% random coil and 20% silk II (anti-parallel β-sheet) structures. When it was soaked in 80% methanol for 30 s, the ratio of silk II changed to 50%. These results explained that the densely packed surface prevented the GOD from leaking.
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