Abstract: After the degummed fiber of silk fibroin derived from Bombyx mori cocoon was dissolved in CaCl₂ ternary solvent system or highly concentrated LiBr solution, three kinds of silk fibroin in liquid could be obtained by means of dialysis. SDS-PAGE analysis results show that three kinds of silk fibroin are of different molecular ranges. The silk fibroin nanoparticles were prepared rapidly from the liquid silk by using water-miscible organic solvents such as acetone. These nanoparticles are insoluble in water but well dispersed and stable in aqueous solution and are globular particles with a size range of 50—120 nm in diameter by means of SEM. L-Asparaginase as a model enzyme was bioconjugated with these nanoparticles by cross-linking agent glutaraldehyde. Activity analysis results indicate that silk fibroin nanoparticles derived from the fibroin by less breakage of peptide chain are more suitable for the bioconjugation of enzymes. The results show that the recovery of the immobilized L-asparaginase was about 44%. Its theromal stability increased evidently and the optimal scale of pH was much wider(pH 6.0—8.0) than that of native L-asparaginase. And the optimal reaction temperature of the modified enzyme was increased about 10 ℃. These preliminary results above indicat that the silk protein nanoparticles are also a good support as silk fibroin membrane. Therefore, the silk fibroin nanoparticles as a new drug release system are of potential values for study and development.

Key words: Silk fibroin nanoparticle, L-Asparaginase, Immobilization enzyme, Cross-linking