Xylanase

About: Xylanase is a research topic. Over the lifetime, 7099 publications have been published within this topic receiving 163793 citations.

Regulation of synthesis of cell wall degrading enzymes by Veticillium albo-atrum and Fusarium oxysporum f. sp. lycopersici☆

Abstract: Induction and catabolite repression of synthesis of cell wall degrading enzymes by the vascular wilt fungi Verticillium albo-atrum and Fusarium oxysporum f. sp. lycopersici have been studied. In cultures containing inorganic salts and tomato stem cell walls each fungus produced a range of extracellular, polysaccharide degrading enzymes. In V. albo-atrum cultures, the enzymes appeared sequentially over 2 to 9 days in the order endopolygalacturonase (endo-PG), exo-arabinanase, endo-pectin-trans-eliminase (endo-PTE), endoxylanase and cellulase; β- d -galactosidase, galactanase and β- d -glucosidase were also produced. Under similar conditions F. oxysporum produced endo-PG, endo-PTE, arabinanase, β- d -galactosidase, xylanase and cellulase. Synthesis of each enzyme was almost always induced specifically by the sugar or uronic acid unit predominant in the specific polymeric substrate for the enzyme. This became evident only when inducers were supplied at rates which prevented their accumulation in cultures. Exceptionally, cellulase was induced by cellobiose but not glucose, and β-galactosidase a and galactanase were induced both by d -galactose and the structurally related l -arabinase. Synthesis was repressed when inducers were present in slight excess of requirements for growth. Synthesis by V. albo-atrum of endo-PG and endo-PTE increased with inducer supply until inducer began to accumulate, then decreased sharply and was almost completely repressed at supply rates three times the optimal value. Synthesis of exo-arabinanase and β-galactosidase decreased as supply of arabinose increased above the optimum but remained at much higher levels relative to those for endo-PG and endo-PTE. Constitutive synthesis of enzymes by V. albo-atrum was also catabolite repressed but to a lesser degree. The significance of induction and catabolite repression in pathogenesis in vascular wilts is discussed.

Xylanase B and an arabinofuranosidase from Pseudomonas fluorescens subsp. cellulosa contain identical cellulose-binding domains and are encoded by adjacent genes.

Abstract: The complete nucleotide sequence of the Pseudomonas fluorescens subsp. cellulosa xynB gene, encoding an endo-beta-1,4-xylanase (xylanase B; XYLB) has been determined. The structural gene consists of an open reading frame (ORF) of 1775 bp coding for a protein of Mr 61,000. A second ORF (xynC) of 1712 bp, which starts 148 bp downstream of xynB, encodes a protein, designated xylanase C (XYLC), of Mr 59,000. XYLB hydrolyses oat spelt xylan to xylobiose and xylose, whereas XYLC releases only arabinose from the same substrate. Thus XYLB is a typical xylanase and XYLC is an arabinofuranosidase. Both enzymes bind to crystalline cellulose (Avicel), but not to xylan. The nucleotide sequences between residues 114 and 931 of xynB and xynC were identical, as were amino acid residues 39-311 of XYLB and XYLC. This conserved sequence is reiterated elsewhere in the P. fluorescens subsp. cellulosa genome. Truncated derivatives of XYLB and XYLC, in which the conserved sequence had been deleted, retained catalytic activity, but did not exhibit cellulose binding. A hybrid gene in which the 5' end of xynC, encoding residues 1-110 of XYLC, was fused to the Escherichia coli pho A' gene (encodes mature alkaline phosphatase) directed the synthesis of a fusion protein which exhibited alkaline phosphatase activity and bound to cellulose.

Enzymes with xylanase activity from aspergillus aculeatus

Abstract: An enzyme exhibiting xylanase activity, which enzyme is immunologically reactive with an antibody raised against a purified xylanase derived from Aspergillus aculeatus, CBS 101.43. The enzyme may be used for degrading plant cell wall components e.g. in the preparation of feed, in baking, in the paper and pulp industry and in connection with separation of wheat into starch and gluten.

Effects of enzymes in fibre‐enriched baking

Abstract: The aim of the present study was to improve the quality of fibre-enriched wheat breads by enzymic treatment of the fibre fraction. The suitability of different enzymes in fibre-enriched baking and their effects on the dietary fibre content and the ratio of insoluble: soluble fibre content of the breads were studied. The enzyme preparations used were a hemicellulolytic culture filtrate of Trichoderma reesei, a specific (pI 9) xylanase of T reesei and Fermizyme, an α-amylase preparation containing a standardised level of hemicellulase activity. Rye bran was extracted in water (10% (w/w) suspension) to determine the solubilities of the β-glucans and pentosans. Addition of T reesei culture filtrate significantly increased the amount of extractable pentosan obtained from nonautoclaved rye bran. Rye bran supplementation (5%) of wheat flour increased the farinograph absorption and dough development time, but had little or no effect on stability and softening of the dough. The added enzymes decreased dough stability and increased softening. Addition of enzymes caused significant differences in the stickiness of the wheat doughs both with (P<0·003) and without (P<0·001) rye bran. Fermizyme significantly increased the stickiness of wheat doughs both with and without rye bran. The baking results of the fibre-enriched breads were improved by the added enzymes. Addition of T reesei culture filtrate increased the specific volume of the wheat breads both with and without rye bran by almost 20%. Enzyme mixtures were more efficient than individual xylanase in softening the bread crumb and reducing the staling rate of wheat breads both with and without rye bran. Incorporation of enzymes reduced the total dietary fibre content of the breads, but at least doubled the amount of soluble pentosan. The proportions of fluorescent cell walls in the breads were detected by microscopical image analysis. Enzyme addition caused the surface area of insoluble cell walls originating from wheat flours to decrease, suggesting that the enzymes exert more effects on wheat endorsperm cell walls than on bran particles. © 1998 SCI.

A novel class of protein from wheat which inhibits xylanases

Abstract: We have purified a novel class of protein that can inhibit the activity of endo-beta-1,4-xylanases. The inhibitor from wheat (Triticum aestivum, var. Soisson) is a glycosylated, monomeric, basic protein with a pI of 8.7-8.9, a molecular mass of 29 kDa and a unique N-terminal sequence of AGGKTGQVTVFWGRN. We have shown that the protein can inhibit the activity of two family-11 endo-beta-1, 4-xylanases, a recombinant enzyme from Aspergillus niger and an enzyme from Trichoderma viride. The inhibitory activity is heat and protease sensitive. The kinetics of the inhibition have been characterized with the A. niger enzyme using soluble wheat arabinoxylan as a substrate. The Km for soluble arabinoxylan in the absence of inhibitor is 20+/-2 mg/ml with a kcat of 103+/-6 s-1. The kinetics of the inhibition of this reaction are competitive, with a Ki value of 0.35 microM, showing that the inhibitor binds at or close to the active site of free xylanase. This report describes the first isolation of a xylanase inhibitor from any organism.