h i g h l i g h t s• Enzymes were immobilized on magnetic nanoparticles by a methioninetag system.• Methionine-tagged immobilized enzymes showed 98% residual specific activity.• The system provided orientational immobilization via the formation of Au-S bonds.
g r a p h i c a l a b s t r a c t a b s t r a c tWe developed a novel technique for immobilizing enzymes on magnetic nanoparticle surfaces by using a methionine-tag system. Au/Fe-oxide composite nanoparticles synthesized through a radiochemical process were used as magnetic nanocarriers. The C-terminus of Tk-subtilisin, a model enzyme, was modified with a methionine tag and mixed with Au/Fe-oxide composite nanoparticles for immobilization via Au-S bonding. Methionine-tagged immobilized enzymes showed 98% residual specific activity, while the untagged enzymes showed 78%. The methionine-tagged immobilized enzymes retained their activities in a wide temperature range of 30-70 • C. Thus, the methionine-tag system provided orientational immobilization via the formation of Au-S bonds, which resulted in structural stability of the immobilized enzymes.
Functionalities of thermoresponsive molecules immobilized on iron-oxide magnetic nanoparticles were non-invasively controlled by the application of alternating magnetic field keeping the solution temperature unchanged. Hydrodynamic particle sizes of iron oxide nanoparticles functionalized with thermoresponsive polymers were successfully controlled. The activity of the thermoresponsive enzymes immobilized on iron oxide was significantly enhanced by the application of alternating magnetic field.
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