Acceleration of protein decomposition by photocatalytic Ti(IV)-doped calcium hydroxyapatite particles and its application for reduction of pathogenic proteins

Acceleration of protein decomposition from single- and mixed-protein solutions on the surface of Ti(IV)-doped calcium hydroxyapatite (TiHap) particles with a Ti/(Ca+Ti) atomic ratio (X _Ti) of 0.10 and 0.20 under ultraviolet (UV) irradiation was investigated. The UV irradiation started immediately after dispersing the TiHap particles in protein solution in a quartz tube (0 h UV method). Lysozyme (LSZ) was steeply decomposed in a LSZ single system by the 0 h UV method. Furthermore, a selective photocatalytic decomposition of LSZ was observed on the mixed-protein system; i.e., only LSZ molecules were decomposed completely from the bovine serum albumin (BSA; 2.5 mg/cm³) − LSZ (1.0 mg/cm³) mixture using TiHap particles. The selective decomposition of pathogenic protein β₂-microglobulin (β₂-MG) from 20 μg/cm³ β₂-MG − 10 mg/cm³ BSA mixture in 1.5 mL × 10⁻⁴ M KCl solution was also examined. The UV irradiation started at 24 h after dispersing TiHap particles in BSA–β₂-MG-mixed solution for attaining the protein adsorption equilibrium (24 h UV method). It was revealed that β₂-MG molecules were entirely destructed by the 24 h UV method by only irradiating UV light to the dispersions for 24 h. The obtained selective decomposition of β₂-MG strongly suggested that TiHap particles can be applied for a blood purification therapy using UV irradiation.