Hydroxyapatite nanoparticles modified with metal ions for xylanase immobilization.

Hydroxyapatite (HA) nanoparticles are promising materials for enzyme immobilization, since they provide a high specific surface area for enzyme loading and can also be modified with metal ions (HA-Me2+) to enable interaction with proteins. The adsorption of proteins on HA-Me2+ has been explored for purification purposes, while the use of this material as a support for the immobilization of enzymes remains to be further investigated. Xylanase is an enzyme of considerable industrial interest, being used in the biofuel, pharmaceutical, pulp, and food & beverage sectors, among others. The immobilization of xylanase can enable recovery of the enzyme after biocatalysis, so that it can be reused several times, hence reducing the costs of industrial processes. Here, a systematic study was performed of the immobilization of xylanase on HA nanoparticles modified with metal ions (Cu2+ and Ni2+). A simple, fast, and efficient immobilization protocol was established using statistical experimental design as a tool, generating derivatives by interactions involving complexation of metals of the support with electron donor groups of the enzyme. The affinity towards xylanase was higher for the HA-Cu2+ support, compared to HA and HA-Ni2+. The pH and temperature profiles for the immobilized enzyme activity remained the same as for the soluble enzyme, indicating that the xylanase did not undergo major changes in its conformational state after immobilization. The HA-Cu2+ support was the most effective in reuse assays, retaining up to 80% activity in the second cycle. The results showed that xylanase could be immobilized on HA nanoparticles modified with Cu2+ and Ni2+ metal ions, using a simple and effective method, indicating the promising potential of the system for applications in different industrial processes.