Immobilization and collection of enzymes by hydroxyapatite/maghemite composite particles with magnetism

Abstract

Apatite nuclei (ApN) were precipitated by raising the pH of simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. The maghemite (£-Fe2O3) particles were attached to the ApN, and the particles were subsequently soaked in SBF adjusted at pH = 7.60, 36.5°C for one day. By this treatment, the ApN induced hydroxyapatite (HA) formation and the £-Fe2O3 particles were encapsulated with HA particles with approximately 12 m in diameter. The specific surface area of thus-obtained HA/Fe2O3 particles was almost 27 times as large as that of the commercially obtained HA particles. Urease or superoxide dismutase (SOD) was immobilized on the surface of the HA/Fe2O3 particles in ultrapure water, and the particles were collected by using a neodymium magnet. It was indicated that more than 90%of urease or SOD was collected by using the HA/Fe2O3 particles. By using the urease immobilized on the HA/Fe2O3 particles, furthermore, urea dispersed in buffered solution almost completely decomposed. As the immobilization efficiency of urease increased, the urea decomposition was promoted.