Purification and characterization of thermophilic xylanase isolated from the xerophytic-Cereus pterogonus sp.

A thermo stable xylanase was purified and characterized from the cladodes of Cereus pterogonus plant species. The enzyme was purified to homogeneity by ammonium sulfate (80%) fractionation, ion exchange and size exclusion chromatography. The enzyme showed a final specific activity of 216.2 U/mg and the molecular mass of the protein was 80 KDa. The optimum pH and temperature for xylanase activity were 5.0 and 80 °C, respectively. With oat spelt xylan as a substrate the enzyme yielded a Km value of 2.24 mg/mL and a Vmax of 5.8 μmol min(-1) mg(-1). In the presence of metal ions (1 mM) such as Co(2+),Mn(2+), Ni(2+), Ca(2+) and Fe(3+) the activity of the enzyme increased, where as strong inhibition of the enzyme activity was observed with the use of Hg(2+), Cd(2+), Cu(2+), while partial inhibition was noted with Zn(2+) and Mg(2+). The substrate specificity of the xylanase yielded maximum activity with oat spelt xylan.