The Carboxylated Multi-walled Carbon Nanotubes/l-Asparaginase Doped Calcium-Alginate Beads: Structural and Biocatalytic Characterization

Abstract

The calcium-alginate/multi-walled carbon nanotube hybrid beads (Ca-ALG/MWCNT-COOH) as a novel kind of matrix were fabricated and characterized in detailed. l-Asparaginase (l-ASNase), which is important chemotherapeutic enzyme-drug in leukemia, was immobilized on the Ca-ALG/MWCNT-COOH hybrid beads. To the best of our knowledge, this is the first study using Ca-ALG/MWCNT-COOH hybrid beads for l-ASNase immobilization. Our characterization investigations displayed that the hybridization between ALG and MWCNT-COOH caused significant changes on the surface morphology and structure. ALG of 0.5% (w/v), CaCl2 of 0.2 M concentration, enzyme of 187.5 U and bead size of 2 mm was found to be best with respect to enzyme loading efficiency. The enzyme was loaded a high yield (97.0%) on these hybrid beads. Remarkably, the tolerance of immobilized enzyme developed towards temperature and pH changes. The maximum activity for the free enzyme was observed at 35 degrees C, pH 7.5, whereas the immobilized enzyme showed maximum activity at 45 degrees C pH 8.5. After immobilization, storage stability of enzyme improved and retained more than 70% of its initial activity after 4 weeks at ~ 30 degrees C as compared with free enzyme which showed only 20% of residual activity. After immobilization, Km value decreased 1.27-fold compared to free counterpart, indicating increased the affinity between the substrate and enzyme. Moreover, immobilized enzyme maintained more than 36% of its original activity even after consecutive 14 reuse. As result, it is worthy of noting that this kind of hybrid materials may become a promising support material for the immobilization of commercial enzymes in areas such as industrial and medical. Graphic