Modification of the Carbohydrate Composition of Sulfite Pulp by Purified and Characterized -Xylanase and 
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- 作者：L. P. Christov ; J. Myburgh ; F. H. O'Neill ; A. Van Tonder ; and B. A. Prior
- 刊名：Biotechnology Progress
- 出版年：1999
- 出版时间：April 1999
- 年：1999
- 卷：15
- 期：2
- 页码：196 - 200
- 全文大小：50K
- 年卷期：v.15,no.2(April 1999)
- ISSN：1520-6033
文摘
Both 
-xylanase and -xylosidase were purified to homogeneity from a xylose-grownculture of Aureobasidium pullulans. Cellular distribution studies of enzyme activitiesrevealed that -xylanase was an extracellular enzyme, during both the exponentialand stationary phases, whereas -xylosidase was mostly periplasmic associated. The-xylanase exhibited very high specificity for xylan extracted from Eucalyptus grandisdissolving pulp, whereas the -xylosidase was only active on p-nitrophenyl xylosideand xylobiose. Comparison of kcat/Km ratios showed that the -xylanase hydrolyzedxylan from dissolving pulp 1.3, 2.1, and 2.3 times more efficiently than Eucalyptushemicellulose B, Eucalyptus hemicellulose A, and larchwood xylan, respectively. The-xylosidase exhibited a transxylosylation reaction during the hydrolysis of xylobiose.When applied on acid sulfite pulp, both enzymes released xylose and hydrolyzed xylanto a different extent. Although -xylosidase (0.4 U/g pulp) liberated more xylose frompulp than -xylanase (4.7 U/g pulp), it was responsible for only 3% of xylansolubilization. Treatment of pulp with -xylanase liberated 51.7 
g of xylose/g andhydrolyzed 10% of xylan. The two enzymes acted additively on pulp and removed 12%of pulp xylan. A synergistic effect in terms of release of xylose from pulp was observedwhen the enzyme mixture of -xylanase and -xylosidase was supplemented with-mannanase. However, this did not result in further enzymatic degradation of pulpxylan. Both -xylanase and -xylosidase altered the carbohydrate composition of sulfitepulp by increasing the relative cellulose content at the expense of reduced hemicellulosecontent of pulp.
-xylanase and -xylosidase were purified to homogeneity from a xylose-grownculture of Aureobasidium pullulans. Cellular distribution studies of enzyme activitiesrevealed that -xylanase was an extracellular enzyme, during both the exponentialand stationary phases, whereas -xylosidase was mostly periplasmic associated. The-xylanase exhibited very high specificity for xylan extracted from Eucalyptus grandisdissolving pulp, whereas the -xylosidase was only active on p-nitrophenyl xylosideand xylobiose. Comparison of kcat/Km ratios showed that the -xylanase hydrolyzedxylan from dissolving pulp 1.3, 2.1, and 2.3 times more efficiently than Eucalyptushemicellulose B, Eucalyptus hemicellulose A, and larchwood xylan, respectively. The-xylosidase exhibited a transxylosylation reaction during the hydrolysis of xylobiose.When applied on acid sulfite pulp, both enzymes released xylose and hydrolyzed xylanto a different extent. Although -xylosidase (0.4 U/g pulp) liberated more xylose frompulp than -xylanase (4.7 U/g pulp), it was responsible for only 3% of xylansolubilization. Treatment of pulp with -xylanase liberated 51.7 g of xylose/g andhydrolyzed 10% of xylan. The two enzymes acted additively on pulp and removed 12%of pulp xylan. A synergistic effect in terms of release of xylose from pulp was observedwhen the enzyme mixture of -xylanase and -xylosidase was supplemented with-mannanase. However, this did not result in further enzymatic degradation of pulpxylan. Both -xylanase and -xylosidase altered the carbohydrate composition of sulfitepulp by increasing the relative cellulose content at the expense of reduced hemicellulosecontent of pulp.