Purification and characterization of Aspergillus β- d-galactanases acting on β-1,4- and β-1,3/6-linked arabinogalactans

• Published in: Carbohydrate polymers Vol. 53; no. 2; pp. 155 - 168
• Main Authors: Luonteri, Elina, Laine, Christiane, Uusitalo, Sanna, Teleman, Anita, Siika-aho, Matti, Tenkanen, Maija
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-08-2003; Elsevier Science
• Subjects: Applied sciences; Aspergillus; Black liquor; endo-β-1,4-galactanase; Exact sciences and technology; Galactan; Kraft pulp; Paper, paperboard, non wovens; Polymer industry, paints, wood; Spent liquors; Wood. Paper. Non wovens; β-1,6-galactanase; endo-β-1,4-galactanase; Aspergillus; β-1,6-galactanase; Kraft pulp; Black liquor; Galactan; Purification; Enzyme; Arabinogalactan endo-1,4-β-galactosidase; Arabinogalactan; Arabinan; Paper industry; Fungi; Characterization; Glycosidases; Spent liquor; Hydrolases; Chemical composition; Fungi Imperfecti; O-Glycosidases; Thallophyta
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/S0144-8617(02)00303-X

Arabinogalactan and arabinan fractions were isolated from kraft pulping black liquor. Both type I and type II arabinogalactans consisting of 1,4- and 1,3-linked β-
d-galactose backbones, respectively, were found. Samples contained more arabino-1,3/6-galactan than arabino-1,4-galactan. Arabinan was mainly 1,5-linked slightly branched polysaccharide. Two enzymes acting on galactans, an
endo-β-1,4-
d-galactanase and a β-1,6-
d-galactanase, were isolated from commercial pectinase preparations produced by
Aspergillus aculeatus and
A. niger, respectively. The purified enzymes showed molecular masses of 38 and 58
kDa, respectively. Based on its N-terminal amino acid sequence the
endo-β-1,4-
d-galactanase was the same as the previously studied GAL1 from
A. aculeatus. It acted on β-1,4-linked galactan, producing a range of galacto-oligosaccharides. It was also able to liberate galactose from a lignin–carbohydrate complex isolated from softwood kraft pulp. No activity was detected towards β-1,3-liked galactan. The β-1,6-
d-galactanase was active on arabino-1,3/6-galactan, liberating galactose and 1,6-β-
d-galactobiose. It was found to be active only on β-1,6-linkages and no detectable hydrolysis of β-1,3-galactose linkages occurred. It also showed no activity on 1,4-β-
d-galactan. However, β-1,6-
d-galactanase was able to liberate arabinose from arabinan. Although chemical pulps contain only a minute quantity of galactans, both galactanases have recently been shown to enhance the bleachability of spruce kraft pulp.