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. [ABSTRACT FROM AUTHOR]