Kinetic characterization of purified laccase from Trametes hirsuta: a study on laccase catalyzed biotransformation of 1,4-dioxane.

OBJECTIVE: Laccase is one of the best known biocatalysts which degrade wide varieties of complex molecules that are both non-cyclic and cyclic in structure. The study focused on enzyme kinetics of a purified laccase from Trametes hirsuta L. fungus and its application on biotransformation of a carcinogenic molecule 1,4-dioxane. RESULTS: Laccase was purified from white-rot fungus T. hirsuta L. which showed specific activity of 978.34 U/mg after the purification fold of 54.08. The stable laccase activity (up to 16 h) is shown at 4-6 pH and 20-40 °C temperature range. The purified enzyme exhibited significant stability for 10 metal ions up to 10 mM concentration, except for Fe2+ and Hg2+. The Cu2+ ion induced laccase activity up to 142% higher than the control at 10 mM concentration. The laccase enzyme kinetic parameters Km was 20 ± 5 µM and 400 ± 60 µM, whereas Kcat was 198.29 ± 0.18/s and 80.20 ± 1.59/s for 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and guaiacol respectively. The cyclic ether 1,4-dioxane (100 ppm) was completely degraded in presence of purified laccase within 2 h of incubation and it was confirmed by HPLC and GC analysis. The oxidation reaction was accelerated by 25, 22, 6 and 19% in presence of 1 mM syringaldehyde, vanillin, ABTS and guaiacol mediators respectively. CONCLUSIONS: In this study, fungal laccase (a natural biocatalyst) based degradation of synthetic chemical 1,4-dioxane was reported for the first time. This method has added advantages over the multiple methods reported earlier being a natural remedy.

Scheelite like NaTb(WO4)2 nanoparticles: Green fluorescence and in vitro cell imaging applications.

This study highlights the investigation of the green fluorescence in NaTb(WO4)2 materials (NaTbW Bulk and NaTbW Nano) synthesized via template free hydrothermal method as a function of particle size and morphology. Herein, we demonstrated the biocompatibility and intracellular green fluorescence of NaTbW Nano samples using HeLa cells for cell imaging applications. Powder X-ray diffraction studies showed that the as synthesized NaTbW Bulk and NaTbW Nano crystallize in the Scheelite like tetragonal crystal system with the I41/a space group. The reaction pH and solvent is observed to play a critical role in determining particle size, shape and morphology of these luminescent materials. Furthermore, size dependent optical properties were systematically studied by diffuse reflectance, steady state photoluminescence; time resolved fluorescence lifetime and quantum yield measurements. Both the materials have shown bright green fluorescence upon UV excitation as a function of particle size. Remarkable high quantum yield of NaTbW Bulk indicated its greater luminescence efficiency and the closer CIE coordinates to the commercial green illuminant suggested their potential use in solid state display systems. On the other hand the observed biocompatibility of NaTbW Nano particles towards mammalian cancer HeLa cells, Staphylococcus aureus, Escherichia coli and the intracellular green fluorescence rightly proved its functionality as active bio-probes. Thus, our work summarize the potential use of these Scheelite like NaTb(WO4)2 material for solid state display and bio-imaging applications.