Isolation,purification, and characterization of thermophilic laccase from the xerophyte <Emphasis Type="Italic">Cereus pterogonus</Emphasis>

Three laccase temperature isoforms were isolated and purified to homogeneity from the xerophyte plant species Cereus pterogonus. This catalytically active protein exhibited an apparent molecular mass of 137 kDa, 90 kDa, and 43 kDa. Under reducing conditions the enzyme yielded a subunit molecular mass of 43 kDa alone, suggesting that the enzyme is a multimer of its subunits. The enzyme exhibited an optimum pH of 10 with 2,6-dimethoxyphenol used as a substrate. The 137 and 90 kDa forms yielded optimum activity at 90°C; whereas the 43 kDa molecular form yielded optimum activity at 60°C. The enzyme kinetic constant Km remained closely similar for all three enzyme forms, whereas Vmax varied by 25 % overall. The catalytic activity remained above its t_1/2 value in excess of the 30 min denaturation assay period at 60°C and 90°C. These high-temperature isoforms of the plant laccase enzyme with alkaline pH optima can find great industrial use.