ISOLATION, PROPERTIES, AND POSTULATED ROLE OF SOME OF THE XYLANASES FROM THE BASIDIOMYCETE SPOROTRICHUM DIMORPHOSPHORUM

Article abstract of DOI:10.1016/0008-6215(83)88049-5

Xylanases excreted by the fungus Sporotrichum dimorphosphorum have been separated by chromatography on DEAE-Shephadex at pH 7 into Fractions I and II.Gel filtration did not further resolve the enzymes, and preparative electrofocusing was necessary to isolate xylanases of pI 7.1, 7.2, 7.35, and 7.95 in fraction I and pI 3.9, 4, 4.4, 4.7, and 5.5 in fraction II.The latter fraction was studied in detail, and afforded two pure xylanases (pI 4.4 and 4.7); the others were contaminated by O-(carboxymethyl)cellulases.The xylanases of pI 3.9, 4, 4.4, and 4.7 had molecular weigts of 32,000 and that of the xylanase of pI 5.5 was 26,000.The optimal reaction temperature was 65-70 deg C for the former enzymes and 50 deg C for the latter.The optimum pH of action was 4.5-5 for all of these xylanases.The xylanases of pI 4.7 and 5.5, the major constituents of the system, exhibit different properties and different values of their Michaelis constants.The end-products of the reaction affect the reactivity of the enzymes.Xylobiose and 4-thioxylobiose are competitive inhibitors of the xylanase of pI 5.5 but they are activators of the xylanase of pI 4.7 in the presence of xylan.This observation is suggestive of a new mechanism for regulation of hydrolysis.