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.
Highlights
Xylan is the major component of hemicellulose, which is abundant in the cell walls of monocot plants and hardwoods
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
F. heterosporum was capable of growing and producing xylanase (6.94 U/ml) in a culture containing barley-brewing residue, which is an inexpensive substrate that is disposed of in large scale from the brewing industry in Brazil. This result indicates that a substrate such as barley-brewing residue, which is rich in cellulosic and non cellulosic polysaccharides, can be efficiently used to induce xylanase production by F. heterosporum (Table 1)
Summary
Xylan is the major component of hemicellulose, which is abundant in the cell walls of monocot plants and hardwoods. Due to the structural complexity of xylan, its complete hydrolysis requires the synergistic action of several enzymes, including the endo-1, 4-β-D-xylanases (EC 3.2.1.8), which are important for cleavage of the glycosidic β-1, 4 bonds of the backbone of xylan to produce short-chain xylooligosaccharides of various lengths; β-xylosidase, αarabinofuranosidase, α-methylglucuronidase and acetyl xylan esterase (Collins et al, 2005; Lafond et al, 2011). These xylanases are classified as Glycosyl Hydrolases. In this study, the influence of thiol compounds on xylanase from F. heterosporum that had been inhibited by heavymetal ions and the recovery of the catalytic activity of metal-ion-inhibited xylanase is reported
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