Abstract

The properties of xylanase purified from Fusarium heterosporum that was grown in barley-brewing residue under solid-state fermentation and the effects of thiol compounds on the reactivation of the metal ion-inhibited xylanase were investigated. Xylanase was purified to homogeneity by ion exchange chromatography, and its molecular mass was estimated to be 19.5 kDa by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The optimum pH for the xylanase was 5.0, and it was stable in acidic pH (4.5 to 5.5), where it retained more than 87% of its activity after 24 h. The optimum temperature was 50°C, and it had a half-life of 53 min at 45°C. The apparent Km and Vmax values for the xylanase were 5.63 mg/ml and 800 µmol/mg/min, respectively. Ba²⁺, Ca²⁺, Mg²⁺ and the thiol compounds β-mercaptoethanol and dithiothreitol (DTT) enhanced xylanase activity, while Hg²⁺, Pb²⁺ and Zn²⁺ strongly inhibited enzyme activity. Furthermore, this xylanase had an alternative mode of regulation in the presence of thiol compounds because the enzyme was able to recover its catalytic activity after inhibition by heavy metal ions.

Key words: Hemicellulase, fungus, solid-state fermentation, barley brewing residue, thiol compounds.

Abbreviation

DTT, Dithiothreitol; SDS-PAGE, sodium dodecyl sulphate polyacrylamide gel electrophoresis.