Sugarcane bagasse was used as an inexpensive alternative carbon source for production of β-xylanases from Aspergillus terreus. The induction profile showed that the xylanase activity was detected from the 6th day of cultivation period. Two low molecular weight enzymes, named Xyl T1 and Xyl T2 were purified to apparent homogeneity by ultrafiltration, gel filtration and ion exchange chromatographies and presented molecular masses of 24.3and 23.60 kDa, as determined by SDS-PAGE, respectively. Xyl T1 showed highest activity at 50 °C and pH 6.0, while Xyl T2 was most active at 45 °C and pH 5.0. Mass spectrometry analysis of trypsin digested Xyl T1 and Xyl T2 showed two different fingerprinting spectra, indicating that they are distinct enzymes. Both enzymes were specific for xylan as substrate. Xyl T1 was inhibited in greater or lesser degree by phenolic compounds, while Xyl T2 was very resistant to the inhibitory effect of all phenolic compounds tested. The apparent km values of Xyl T2, using birchwood xylan as substrate, decreased in the presence of six phenolic compounds. Both enzymes were inhibited by N-bromosuccinimide and Hg(2+) and activated by Mn(2+). Incubation of Xyl T1 and Xyl T2 with L-cysteine increased their half-lives up to 14 and 24 h at 50 °C, respectively. Atomic force microscopy showed a bimodal size distribution of globular particles for both enzymes, indicating that Xyl T1 is larger than Xyl T2.
Keywords: Aspergillus terreus; Atomic force microscopy; Mass spectrometry; Phenolic compounds; β-Xylanase purification.
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