Xylose Dehydrogenase Immobilized on Ferromagnetic Nanoparticles for Bioconversion of Xylose to Xylonic Acid.

d-Xylonic acid (XA), derived from pentose sugar xylose, is a multifunctional high-value chemical with a wide range of applications in the fields of medicines, food, agriculture and is a valuable chemical reagent for the synthesis of other useful commodity chemicals. In the bacterial system, xylose dehydrogenase (XDH) catalyzes the oxidation of d-xylose into d-xylonolactone, consuming NAD or NADP as a cofactor. The d-xylonolactone then undergoes auto-oxidation into d-xylonic acid. Herein, the XDH enzyme overexpressed in is purified and immobilized on ferromagnetic nanoparticles, effectively converting xylose into xylonic acid. Parameters deciding the bioconversion were statistically optimized and obtained a maximum of 91% conversion rate. Kinetic parameters of immobilized xylose dehydrogenase showed a 2-fold increase in the maximum velocity of the reaction and catalytic efficiency compared to free enzyme. The operational stability test for the enzyme-nanoparticle conjugate retained 93% relative activity after 10 successive experiments, exhibiting the good recyclability of the biocatalyst for XA production.