Purification and characterization of a thermostable xylanase from the brown-rot fungus Laetiporus sulphureus

摘要

A thermostable extracellular xylanase was purified and characterized from brown-rot basidiomycete Laetiporus sulphureus,cultivated on biologically pretreated Pinus densiflora biomass.After three consecutive purification steps using DEAE,Mono Q,and Superdex 75 columns,the xylanase specific activity was found to be 72.4 U/mg,nine fold higher than that of the crude culture solution,purity was 96%,and the molecular mass determined to be 693 kDa.The optimal pH and temperature for xylanase activity were 3.0 and 80°C,respectively.Although activity of xylanase was highest at 80 °C,it showed highest thermostability at 60°C,retaining approximately 97% of its relative activity following incubation for 4 h.In the presence of 5 mM solution of CaCl2,the relative xylanase activity increased by 35.9%;however,it decreased significantly in the presence of 10 mM solution of Cu~(2+).Among the xylan-based substrates tested,purified L.sulphureus xylanase showed the highest activity on beechwood xylan.Thin-layer chromatography(TLC)experiments revealed that purified L.sulphureus xylanase is an endoxylanase that hydrolyzes xylotriose,xylotetraose,and xylopentaose but not xylobiose.