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. Ba 2+ , Ca 2+ , Mg 2+ and the thiol compounds β-mercaptoethanol and dithiothreitol (DTT) enhanced xylanase activity, while Hg 2+ , Pb 2+ and Zn 2+ 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.

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The Neurospora crassa exo‐1 mutant produced maximum extracellular glucoamylase activity in media supplemented with starch as the sole carbon source. The apparent molecular mass of the enzyme was 82 kDa (SDS‐PAGE and gel filtration). The enzyme was a glycoprotein with 5.1 % carbohydrate content and exhibited a temperature optimum of 60 °C. The pH optima were 5.4 and 5.0 for glucoamylase and maltase activities, respectively. Cu2+ inhibited maltase activity while Mn2+ stimulated glucoamylase activity. The purified enzyme hydrolyzed branched substrates more efficiently than linear substrates. Starch was the best substrate utilized and amylose was hydrolyzed faster than maltose. Kinetic experiments suggested that maltose and starch were hydrolyzed at the same catalytic site.

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