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

We aimed to establish enzyme immobilization technology using the maghemite/hydroxyapatite (Fe2O3/HA) composite particles as enzyme immobilization carriers and to clarify the enzyme adsorption characteristics of the composite particles. Seven kinds of enzymes with various isoelectric points (pI) were immobilized on the Fe2O3/ HA composite particles in buffered solution adjusted at pH = 7.40 or pH = 10.0, 36.5 °C. Effects of the enzyme pI and the solution pH on the immobilization were investigated. In both of the two kinds of buffered solutions, there was an increase or decrease distribution with a maximum local value for pH-pI , which indicated the charge state of the enzymes. The interaction between HA on the composite particles and adsorbed enzymes was expected to be the largest when pH-pI = 12. It was suggested that -chymotrypsin, whose adsorbed amount was the most among the seven kinds of the enzymes, in addition, formed a monolayer on the surface of the composite particles in the buffered solution at pH = 7.40, 36.5 °C.