Dependence property of isoelectric points and pH environment on enzyme immobilization on maghemite/hydroxyapatite composite particles

(a) Adsorption isotherm and (b) Langmuir’s plots of ¡chymotrypsin on Fe2O3/HA composite particles in PBS.

Fig. 6.

«pH-pI«. This suggested that the immobilization of the

enzyme on HA was not dominated by the interaction of the

electric double layer but was caused by various factors

such as van der Waals forces and local ionic interactions.

The immobilization efficiency of ¡-chymotrypsin was the

highest for both solvents at pH = 7.40 and pH = 10.0,

36.5 °C, where «pH-pI« = 1­2. This suggested that the

interaction between the HA and the enzyme is the largest

when «pH-pI« = 1­2. The prepared Fe2O3/HA composite

particles showed the possibility of immobilizing various

kinds of enzymes with high efficiency by using solvents

that make «pH-pI« = 1­2. Alpha-chymotrypsin, which

showed the most immobilization efficiency, was suggested

to form a monolayer on the Fe2O3/HA composite particles

in PBS. This study is expected to be helpful for contributing to the development of novel enzyme immobilization carriers with both enzyme affinity and collection

advantage by magnetism.

Acknowledgments This work was partly supported by

Kansai Research Foundation for Technology Promotion,

Japan.

80

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