Development and catalytic characterization of L-asparaginase nano-bioconjugates

The present paper describes efficient immobilization of L-glutaminase free L-asparaginase for developing a new therapeutic system for anticancer therapy. L-asparaginase (L-ASNase) was covalently immobilized on the functionalized aluminum oxide nanoparticles (AONP) and titanium oxide nanoparticles (TONP). The nano-bioconjugates (AONP-ASNase and TONP-ASNase) were characterized by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR) and UV–Vis spectral analysis that revealed the successful immobilization. The nano-bioconjugates were optimally active at pH 7.0 and 40 °C. TONP-ASNase activity was enhanced in the presence of NH4+ (160%) and Mn2+ (165%) while AONP-ASNase bioconjugates showed increased relative activity with ethyl acetate (142%) and toluene (160%). The nano-bioconjugates displayed excellent reusability and maintained >90% average activity after nine successive cycles. Maximum cytotoxicity (61%) was noticed with AONP-ASNase (10 μg/ml) against human leukemia MOLT-4 cells. Regarding kinetic values, AONP-ASNase showed better affinity (Km 1.9 μmol) to L-asparagine as compared to free L-ASNase. After 23 days storage at 37 °C, bioconjugates retained 40% residual activity while free L-ASNase was completely deactivated. Thermodynamic characterization revealed higher conversion rate of the E-S complex in case of nano-bioconjugates.