Novel alkali-thermostable xylanase from Thielaviopsis basicola (MTCC 1467): Purification and kinetic characterization

A novel extracellular alkali-thermostable xylanase was purified to an apparent homogeneity from the submerged fermented culture filtrate of Thielaviopsis basicola MTCC 1467, wherein, the fungus was fed with rice straw as prime carbon source. SDS-PAGE analysis of the xylanase showcased molecular weight of ∼ 32 kDa. This extracellular protein macromolecule had maximum xylanolytic activity at pH 5.5 and 60°C, and was stable in the range of pH 5.0-10.0 for 5 days retaining >70% activity. The enzyme was stable at 30-50°C for 5h retaining >85% activity and further by retaining 70% activity at 60°C for 2h. The enzyme deactivation constants (kd) were in range of 0.41-1.3. The kinetic experiments specified that the enzyme had Km and Vmax values of 1.447 ± 0.22 mg mL(-1) and 60.04 ± 1.25 IU mL(-1), respectively, for xylan. The purified xylanase was significantly inhibited by Cu(2+) and Zn(2+) (∼ 58%), whilst Ca(2+) and Na(+) ions displayed partial inhibition (<8%) Intriguingly, the K(+) and Mn(2+) ions enhanced the activity by about ∼ 10%. Both SDS and EDTA reduced its activity by ∼ 20%.