Chitosan Modified PSt-GMA Microspheres With/Without Spacer-Arms as Carriers: Their Influences on Kinetics, Stability, Optimal pH, Adsorption Behavior of Immobilized Trypsin

Abstract

A series of microspheres, chitosan modified PSt-GMA microspheres with/without the spacer-arms, have been used as carriers to study related properties about immobilized trypsin, such as isothermal adsorption, stability, kinetics and optimal reaction pH. The experimental results showed that the immobilization process could fit the Freundlich model rather than the Langmuir model, indicating the real adsorption behavior was more complex than the ideal adsorption model. In addition, Km values of trypsin immobilized onto M5 or M8 were closer to that of free enzyme and lower than that onto other microspheres, suggesting the trypsin immobilized onto M5 or M8 possessed a higher affinity to substrate. Furthermore, the thermal and operational stabilities of immobilized trypsin, particularly onto M5 or M8, were enhanced compared to that of free trypsin. Compared to free trypsin, the optimal pH of immobilized trypsin didn't change; however,its pH profile was broader. These results have proved that chitosan modified microspheres could keep the conformation and activity of enzyme as well as enhance enzyme's properties. Therefore, it has potential application in high throughput screening of drugs (HTS) based on the scintillation proximity assay (SPA) method.