We 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 degrees 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. (C) 2014 Elsevier B.V. All rights reserved.
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