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Xylanases from the Dutch elm disease pathogens Ophiostoma ulmi and Ophiostoma novo-ulmi

Author: Binz T.   Canevascini G.  

Publisher: Academic Press

ISSN: 0885-5765

Source: Physiological and Molecular Plant Pathology, Vol.49, Iss.3, 1996-09, pp. : 159-175

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Abstract

Ophiostoma novo-ulmi and O. ulmi , the dimorphic pathogens causing Dutch elm disease, both secreted similar amounts of xylanase into the culture medium when grown on birchwood xylan, water-insoluble xylan or elm sapwood but on elm sapwood, the amount of enzyme activity was 3-4 times lower than on the xylans. In neither species, did glucose stimulate xylanase accumulation although arabinose did. No significant difference in extracellular beta-xylosidase between O. ulmi and O. novo-ulmi could be observed. Furthermore, both species secreted alpha-arabinosidase and beta-glucosidase into the medium. O. novo-ulmi (isolate CKT-11) was shown by Q-Sepharose chromatography to form two distinct xylanase enzymes, named xylanase I and II according to their elution pattern from this system. The two xylanases were purified to homogeneity by subsequent molecular size exclusion chromatography.The M r of xylanase I and II were 38 and 22 kDa, respectively, by SDS-PAGE and 19 kDa by gel filtration. The pI was greater than 9.2 for xylanase I and 4.2 for xylanase II as determined by chromatofocusing. Both enzymes mainly yielded xylobiose and xylose upon incubation with water-insoluble xylan and were inactive towards pNP-alpha-arabinose, pNP-beta-xylose, pNP-beta-galactose and pNP-beta-glucose. The pH optimum of activity was 5.2 for xylanase I and 4.0 for xylanase II whereas the temperature optimum was 60 #°C for both enzymes.

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