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

Porous SiO2 nanospheres are prepared and loaded with platinum (Pt) nanoparticles (Pt&SiO2). The Pt&SiO2 nanospheres are coated with a zirconium-based coordination polymer (Pt&SiO2&Zr-cp). Etching of the core SiO2 with NaOH produces hollow nanospheres Pt&h-SiO2&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-SiO2&Zr-cp possesses two-enzyme catalysis capability. The adsorbed DAAO catalyzes oxidative deamination of d-amino acids, and hydrogen peroxide (H2O2) is evolved as a byproduct. The loaded Pt nanoparticles possess peroxidase activity, decomposing H2O2 into H2O and O2. Thus, the byproduct inhibitory effect can be minimized. In addition, the generated dioxygen O2 can be used to oxidize the reduced cofactor FDA of the adsorbed DAAO. The hybrid DAAO&Pt&h-SiO2&Zr-cp was applied for catalytic deamination of d-alanine and exhibited a catalytic efficiency more than four times that of free DAAO.