RESUMO
The present study describes the one-step purification and biochemical characterization of an endo-1,4-ß-xylanase from Aspergillus tamarii Kita. Extracellular xylanase was purified to homogeneity 7.43-fold through CM-cellulose. Enzyme molecular weight and pI were estimated to be 19.5kDa and 8.5, respectively. The highest activity of the xylanase was obtained at 60°C and it was active over a broad pH range (4.0-9.0), with maximal activity at pH 5.5. The enzyme was thermostable at 50°C, retaining more than 70% of its initial activity for 480min. The K0.5 and Vmax values on beechwood xylan were 8.13mg/mL and 1,330.20µmol/min/mg of protein, respectively. The ions Ba2+ and Ni2+, and the compounds ß-mercaptoethanol and DTT enhanced xylanase activity, while the heavy metals (Co2+, Cu2+, Hg+, Pb2+ and Zn2+) strongly inhibited the enzyme, at 5mM. Enzymatic hydrolysis of xylooligosaccharides monitored in real-time by mass spectrometer showed that the shortest xylooligosaccharide more efficiently hydrolyzed by A. tamarii Kita xylanase corresponded to xylopentaose. In agreement, HPLC analyzes did not detect xylopentaose among the hydrolysis products of xylan. Therefore, this novel GH11 endo-xylanase displays a series of physicochemical properties favorable to its application in the food, feed, pharmaceutical and paper industries.
