Institute of Biochemistry and Biotechnology, University of the Punjab, Lahore, 54590, Pakistan.
World J Microbiol Biotechnol. 2012 Feb;28(2):513-22. doi: 10.1007/s11274-011-0842-z. Epub 2011 Jul 17.
Delignification efficacy of xylanases to facilitate the consequent chemical bleaching of Kraft pulps has been studied widely. In this work, an alkaline and thermally stable cellulase-less xylanase, derived from a xylanolytic Bacillus subtilis, has been purified by a combination of gel filtration and Q-Sepharose chromatography to its homogeneity. Molecular weight of the purified xylanase was 61 kDa by SDS-PAGE. The purified enzyme revealed an optimum assay temperature and pH of 60°C and 8.0, respectively. Xylanase was active in the pH range of 6.0-9.0 and stable up to 70°C. Divalent ions like Ca(2+), Mg(2+) and Zn(2+) enhanced xylanase activity, whereas Hg(2+), Fe(2+), and Cu(2+) were inhibitory to xylanase at 2 mM concentration. It showed K ( m ) and V ( max ) values of 9.5 mg/ml and 53.6 μmol/ml/min, respectively, using birchwood xylan as a substrate. Xylanase exhibited higher values of turn over number (K (cat)) and catalytic efficiency (K (cat)/K (m)) with birchwood xylan than oat spelt xylan. Bleach-boosting enzyme activity at 30 U/g dry pulp displayed the optimum bio-delignification of Kraft pulp resulting in 26.5% reduction in kappa number and 18.5% ISO induction in brightness at 55°C after 3 h treatment. The same treatment improved the pulp properties including tensile strength and burst index, demonstrating its potential application in pre-bleaching of Kraft pulp.
木聚糖酶对 kraft 浆进行脱木质素处理，以促进后续的化学漂白，这一方法已得到广泛研究。本研究中，从木聚糖降解芽孢杆菌中分离出一种碱性、热稳定的无纤维素酶木聚糖酶，通过凝胶过滤和 Q-琼脂糖层析对其进行了分离纯化，达到了均一性。SDS-PAGE 显示该木聚糖酶的分子量为 61 kDa。该酶的最适反应温度和 pH 分别为 60°C 和 8.0。木聚糖酶在 pH6.0-9.0 的范围内具有活性，在 70°C 以下稳定。二价离子如 Ca(2+)、Mg(2+)和 Zn(2+)能增强木聚糖酶的活性，而 Hg(2+)、Fe(2+)和 Cu(2+)在 2 mM 浓度下对木聚糖酶有抑制作用。该酶以桦木木聚糖为底物时，K ( m )和 V ( max ) 值分别为 9.5 mg/ml 和 53.6 μmol/ml/min。木聚糖酶对桦木木聚糖的比活力（K (cat)/K (m)）和周转数（K (cat)）均高于大麦芽黑麦草木聚糖。在 30 U/g 干浆的用量下，该酶具有良好的助漂效果，使 kraft 浆的卡伯值降低了 26.5%，在 55°C 下反应 3 h 后，白度提高了 18.5%ISO。该处理还改善了纸浆的物理性能，包括抗张强度和耐破指数，表明其在 kraft 浆的预漂白中有潜在的应用价值。
