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 (£-Fe 2 O 3 ) 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 £-Fe 2 O 3 particles were encapsulated with HA particles with approximately 12¯m in diameter. The specific surface area of thus-obtained HA/Fe 2 O 3 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/Fe 2 O 3 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/Fe 2 O 3 particles. By using the urease immobilized on the HA/Fe 2 O 3 particles, furthermore, urea dispersed in buffered solution almost completely decomposed. As the immobilization efficiency of urease increased, the urea decomposition was promoted.

Dependence property of isoelectric points and pH environment on enzyme immobilization on maghemite/hydroxyapatite composite particles

“…In the previous study, we investigated urease immobilization on Fe 2 O 3 /HA composite particles by investigating the amount of nickel, which exists an active center of urease, using inductively coupled plasma atomic emission spectroscopy. 20) This study showed a similar level of urease immobilization.…”

“…In the previous study, we fabricated Fe 2 O 3 /HA composite particles using ApN obtained by raising the pH of SBF to 8.60, 25.0 °C without raising the temperature. 20) In this study, we fabricated them using ApN by raising the pH of SBF to 8.40 and subsequently raising the temperature by microwave. However, the material morphology of the Fe 2 O 3 /HA composite particles was not so changed only by changing the ApN preparation condition in this experimental system.…”

“…The previous study examined the urease activity immobilized on the Fe 2 O 3 /HA composite particles. 20) Although the decomposition speed of urea was slower than the not-immobilized urease, it was clarified that the immobilized urease decomposed urea almost entirely in the aqueous solution. 20) However, the activity of the immobilized other enzymes, such as basic protein, has not been investigated yet.…”

“…In the previous study, for example, we fabricated HA capsules by attaching ApN to the surface of core materials and immersing them in SBF, in which HA induced by the ApN covered the entire surface of the core materials. 19) The Fe 2 O 3 /HA composite particles, which are HA particles containing maghemite (£-Fe 2 O 3 ) particles, adsorb enzymes on the surface of the particles by the biomolecule adsorption property of HA and the adsorbed enzymes catalyze chemical reactions. By using £-Fe 2 O 3 particles as the core microparticles and making the HA magnetic, it can be quickly recovered from the solution by magnetic force.…”

“…In the previous study, we immobilized urease on Fe 2 O 3 / HA composite particles and fabricated immobilized enzyme capsules for hydrolyzing urea. 20) However, the physical properties and characteristics of the enzyme and the effect of the surrounding environment on the adsorption property of the enzyme have not been clarified. In the previous study, for example, we investigated enzyme immobilization behavior on the Fe 2 O 3 /HA composite particles and commercially obtained rod-type HA particles in phosphate-buffered saline (PBS).…”