Characterization of xerophytic thermophilic laccase exhibiting metal ion-dependent dye decolorization potential.

Five laccase enzyme isoforms were isolated and purified to homogeneity from the cladodes of xerophytic Cereus pterogonus and Opuntia vulgaris plant species. Catalytic activity of all isoforms was enhanced 40 % by 1 mM Cu(2+) and 1 mM Mn(2+), whereas the activity was inhibited 100 % by 10 mM Fe(2+). Enzyme was found stable in 4 M urea and exhibited inactivity of 50 % in 8 M urea concentration. Ethylenediaminetetraacetic acid and cysteine-HCl were able to completely inhibit the enzyme activity at 1 mM and 100 μM, respectively. Preheated enzyme samples showed enhanced and stable catalytic activity in the presence of divalent cations over a period of 30 min compared with controls. In the presence of metal ions (1 mM Cu(2+) and 1 mM Mn(2+)), the preheated enzyme forms (60-90 °C) achieved 97 % of Malachite green and 98.75 % of Indigo blue (both at 2 %, w/v) dye decolorization in 12 h.