D-Xylanases

Two endo- - 4)-j8-D-xylanases (mol. wts. 2.4 x 10 and 4.1 x 10 ) have been shown to be produced by Aspergillus niger. The smaller species in electrophoretically homogeneous form (p/ 4.2, pH optimum 4.2 for carboxy-methylxylan) split arabinoglucuronoxylan to xylo-oligosaccharides but did not hydrolyse xylobiose. 

Six exo-0 - 4)-)3-D-xylanases have been shown to occur in Aspergillus niger. One of these, in electrophoretically homogeneous form (p/ 4.6, mol. wt. 3.0 X 10, pH optimum 3 for methyl )5-D-xylopyranoside), split off D-xylose from the ends of the D-xylan chains of xylotriose, etc., and exhibited high transglycosylase activity. 

Enzyme preparations active against crystalline cellulose, marble-milled filter paper, carboxymethylcellulose (CM-cellulose), hemicellulose, and D-xylan have been obtained from cultures of Ruminococcus flavefaciens. Carboxymethyl cellulase and D-xylanase activities were present in a high molecular weight complex (see p. 461). 

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The value and potential usefulness of a new enzyme depends on its properties and the extent to which it has been characterized. The initial characterization of an enzyme often involves the determination of its pH optimum, stability, gross physical properties, and substrates. The enzymes of L. edodes, typically show pH optima between 3.5 and 5.0, maximal activity at 50 to 60"C, little activity loss until over 70"C, and high relative specific activities (9,14). Below we will highlight some of the other characteristics determined for the major ligninase, p-(l,4)-D-xylanase, and a-(l,3)-L-arabinosidase purified from wood-grown cultures of L. edodes. 

Catalytic Properties and Partial Amino Acid Sequence of an Actinomycete Endo-(l—>4)-/3-D-Xylanase from Chainia Species... 

Of the related polysaccharides mentioned earlier (see p. 267), only arabinoxylans have been examined in any detail by enzymic methods. Goldschmid and Perlin153 studied the fine structure of wheat arabinoxylan by using the /3-D-xylanase from Streptomyces QMB 814. Their results indicated that arabinoxylan molecules are mainly constituted of highly branched regions in which isolated and paired L-arabinosyl (A) branches are separated by single D-xylosyl (X) residues, as shown in 12, but that, at unequal intervals (averaging... 

Xylans and substituted xylans are susceptible to hydrolysis by endo-(l - 4)-/3-D-xylanase (EC3.2.1.8). Reaction of this enzyme with (1- 4)-/3-d-... 

Further information on the fine structure of arabinoxylan should be forthcoming when hydrolysis is performed with a purified (l- 4)-/S-D-xylanase, such as that from Cryptococcus albidus,60 62 whose subsite-... 

Unlike the xylans already discussed, Rhodymenia palmata /3-D-xylan contains mixed (l- 3) and (l- 4) linkages. On reaction with a cellulase that had /S-D-xylanase activity,74 a series of (l- 4) and mixed-linkage xylosaccharides was produced that included (1 - 4)-0-xylo-biose, -triose, -tetraose, and a mixed-linkage trisaccharide, namely, 32-0-/3-D-xylosyl-xylobiose (17). endo-(l - 4)-/3-D-Xylanase has been shown62 to catalyze... 

Lin, J., Ndlovu, L. M., Singh, S., and Pillay, B., Purification and biochemical characteristics of beta-D-xylanase from a thermophilic fungus, Thermomyces lanuginosus-SSBP. Biotechnol Appl Biochem 1999, 30 (Pt 1), 73-9. 

A comprehensive review on D-xylanases and their degradation of D-xylans was written by Sorensen5 in 1957, and since then, brief reviews of the same subject have been written in English by Timell6 and in Japanese by Fukui7 (1961) and Sasaki8 (1971). Work on D-xylanases from 1957 onwards will, therefore, be discussed in detail in this article. 

D-Xylanases have been reported to be produced by several strains of bacteria from marine environments,140,141 such as sea water and marine-bottom sediments, and by green, brown, and red algae (seaweeds). The enzymes have also been isolated from terrestrial fungi, for example, Aspergillus batatae,142 Chaetomium globosum,142 and Irpex lacteus.143 These bacteria and fungi were found to produce both (1 -> 3)- and (1 - 4)-/3-D-xylanases, which were secreted extracellularly. 

Of the 64 strains of (1 — 3)-/J-D-xylan-decomposing marine bacteria (unidentified) examined, at least 40 possessed potent (1 — 3)-/3-D-xylanase activity, and 36 strains were also capable of hydrolyzing (1 -> 4)-/3-D-xylans (see Table XVIII). 

Substrates used in the procedure for the assay of (1— 3)-j3-d-xylanase activity have normally been (1 —> 3)-/3-D-xylans from marine... 

The (1 - 3)-/3-D-xylanase from Chaetomium globosum142 was purified by several fractionation steps employing ammonium sulfate and acetone, and the purified preparation resulting was shown to be free from a-amylase, cellulase, and (1 — 4)-/3-D-xylanase activities, and to have undergone a 106-fold purification. Whether this preparation was homogeneous was not indicated, but it has been used in study of mode of action on (1 — 3)-j8-D-xylan. 

The (1 — 3)-/3-D-xylanase system of lrpex lacteus143 was resolved into nine components by zone electrophoresis at pH 8.7, but each component was found to be contaminated with (1 — 3)- and (1 — 4)-/3-D-glucanase, amylase, and (1 — 4)-j8-D-xylanase activities. None of these components were purified further. 

The physicochemical properties of (1 — 3)-/3-D-xylanases have not yet been reported. 

D-Xylan was hydrolyzed within 1 hour to a limit of 93-95%, and the incomplete hydrolysis was associated with the production, in the hydrolyzate, of X2 (which, as already mentioned, is only slowly degraded to D-xylose). (1 — 3)-/3-D-Xylanases of the endo type have not been detected. 

In this Section, the term xylanase will refer to those enzymes capable of hydrolyzing the (1 — 4)-/3-D-xylopyranosyl linkages of the (1 — 4)-/3-D-xylans, namely, arabinoxylan, arabinoglucuronoxylan, arabino-4-O-methyl-D-glucuronoxylan, and glucuronoxylan. D-Xylanases of this type have been assigned the Enzyme Commission numbers 3.2.1.8 [(1 — 4)-/3-D-xylan xylanohydrolase, endo-xylanase] and 3.2.1.37 [(1 —> 4)-/3-D-xylan xylohydrolase, exo-xylanase]. 

In the invertebrate crustaceans Astacus fluviatilis and Homarus vulgaris, the hepatopancreas gland has been shown124 to be a source of D-xylanase in their digestive juices. D-Xylanases have also been... 

These references contain a comprehensive list of bacterial and fungal strains and species that have been screened for the production of D-xylanase, but that are too numerous to include in this Table. 

Various xylophagic insects have also been found to contain D-xylanases. However, the origin of these enzymes has not been determined, and they may be derived either from cells of the digestive tract, or from protozoal symbionts inhabiting the digestive tract. 

Most of the bacteria and fungi listed in Table XIX produce D-xylanases that are secreted extracellularly. However, some microorganisms (for example, rumen bacteria38-41,212-214 and protozoa,43-47,218 Sporocytophaga myxococcoid.es,0 and Aspergillus niger182) also produce D-xylanases intracellularly. 

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