d-Amino Acid Oxidase Immobilized on Pt Nanoparticle-Loaded Porous SiO₂ Nanospheres Coated with a Zirconium-Based Coordination Polymer for Catalytic Deamination of d-Alanine

Abstract

Porous SiO 2 nanospheres are prepared and loaded with platinum (Pt) nanoparticles (Pt&SiO 2 ). The Pt&SiO 2 nanospheres are coated with a zirconium-based coordination polymer (Pt&SiO 2 &Zr-cp). Etching of the core SiO 2 with NaOH produces hollow nanospheres Pt&h-SiO 2 &Zr-cp. D-Amino acid oxidase (DAAO) with hexahistidine tags was absorbed onto the hollow nanospheres strongly, by utilizing the coordinative interactions between Zr(IV) and the hexahistidine tags. The conjugate DAAO&Pt&h-SiO 2 &Zr-cp possesses two-enzyme catalysis capability. The adsorbed DAAO catalyzes oxidative deamination of D-amino acids, and hydrogen peroxide (H 2 O 2 ) is evolved as a byproduct. The loaded Pt nanoparticles possess peroxidase activity, decomposing H 2 O 2 into H 2 O and O 2 . Thus, the byproduct inhibitory effect can be minimized. In addition, the generated dioxygen O 2 can be used to oxidize the reduced cofactor FDA of the adsorbed DAAO. The hybrid DAAO&Pt&h-SiO 2 &Zr-cp was applied for catalytic deamination of D-alanine and exhibited a catalytic efficiency more than four times that of free DAAO.