Document Type : Research Paper
Authors
1
Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran
2
Laboratory of Bioanalysis, Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran
3
Department of Microbial Biotechnology, School of Biology, College of Science, University of Tehran, Tehran, Iran
Abstract
L-Asparaginase converts L-asparagine to L-aspartic acid and causes cancer cells to starve. The main idea of the current study was to improve the biochemical properties of this enzyme using immobilization onto modified magnetic nano-particles (NPs). To this end, Fe3O4 NPs were synthesized, coated with an Au shell, and conjugated with cysteine. The formation of NPs and core-shell structures and their morphology were confirmed using Fourier Transform Infrared spectroscopy (FTIR), Energy Dispersive X-Ray (EDX), VU-Vis, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Also, Circular Dichroism (CD) and fluorescence spectroscopy were employed for the analysis of the secondary and tertiary structures of the immobilized L-ASNase. The alterations in the kinetic parameters of the immobilized enzyme were analyzed using a Lineweaver-Burk plot. The results of instrumental chemistry analysis confirmed the formation of NPs and core-shell structure, and cysteine binding with the core-shell. Based on CD and fluorescence results, no significant changes were observed in the secondary and tertiary structures of the immobilized enzyme compared to the free one. Kinetic parameters of the immobilized enzyme improved compared to the free enzyme so that Km decreased from 4.43±0.05 to 3.75±0.12 mM and Vmax increased from 187.23±11 to 224.78±16 μM min-1mg-1. Also, the stability of the immobilized enzyme improved with acidic and alkaline pH values compared to the free one at temperatures higher than 50 0C. In addition, the reusability of the immobilized enzyme was superior to the free enzyme, with the immobilized enzyme maintaining 72% of its activity after 15 cycles of catalytic reaction. The immobilized enzyme showed an 86% residual activity after 120 min incubation with trypsin, which was higher than the free enzyme (37%). According to the results of this study, immobilization of L-ASNase onto magnetic NPs can be an efficient strategy to enhance the biochemical properties of this enzyme.
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