Decomposition of proteins by photocatalytic Ti(IV)-doped calcium hydroxyapatite particles

The decomposition of protein molecules on the surface of Ti(IV)-doped calcium hydroxyapatite (TiHap) particles with a Ti/(Ca + Ti) atomic ratio among 0–0.20 under UV irradiation of 365 nm in wavelength was disclosed. The acidic bovine serum albumin (BSA), neutral myoglobin (MGB) and basic lysozyme (LSZ) were employed as a model of pathogenic proteins. The photocatalytic activities of TiHap particles were estimated from the decomposition of each protein under 1 mW/cm2 UV irradiation dispersed in 10 mL quartz tube. The concentrations of each protein in the supernatant after centrifugation during the UV irradiation were determined both by a HPLC and a SDS-Polyacrylamide Gel Electrophoresis (SDS-PAGE) analysis methods. No change in BSA concentration ([BSA]) by UV irradiation was observed for all the unheated original TiHap particles with low photocatalytic activity. The similar results were observed for the systems employed heat treated particles endowed a high photocatalytic activity by heat treatment at 650 °C for 1 h. These results indicated that the decomposition of BSA molecules is hard to take place. The heme structured MGB molecules are decomposed by UV irradiation irrespective of the presence of TiHap particles. In the case of heat treated particles, MGB molecules were further decomposed by the UV irradiation. The strongest photocatalytic activity was observed for the decomposition systems of LSZ by using heat treated particles. In this system, all the TiHap particles completely decomposed LSZ molecules after started the UV irradiation. It was concluded that the ability of decomposition of proteins is strongly related to the molecular weight and rigidity of proteins molecules. The LSZ molecule with low molecular weight and rigid structure was easily decomposed on the surface of heat treated TiHap particles under UV irradiation.