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 Escherichia coli 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.