Simultaneous refolding, purification and immobilization of xylanase with multi-walled carbon nanotubes

Multi-walled carbon nanotubes were used as refolding aid for xylanase unfolded with 8 M urea. The hydrophobic surface of the nanotubes enabled the binding, refolding, purification and simultaneous immobilization of the enzyme. While 55% activity could be regained while working with the denatured form of a purified preparation of xylanase, 92% activity could be obtained with the commercial preparation of xylanase in 8 M urea. These activities were obtained with refolded xylanase bound to the carbon nanotubes. Hence an immobilization efficiency of 0.92 was observed. The FT-IR spectroscopy showed that alpha-helical content of xylanase decreased from 17% to 14%, beta-sheet content increased from 53% to 61% and beta-turns decreased from 20% to 15% upon immobilization on the nanotubes. The refolded xylanase molecule bound to the carbon nanotube gave various secondary structure contents very similar to the bound (to carbon nanotubes) native xylanase.