Isolation, properties, and postulated role of some of the xylanases from the basidiomycete Sporotrichum dimorphosphorum

Abstract

Xylanases excreted by the fungus Sporotrichum dimorphosporum have been separated by chromatography on DEAE-Sephadex 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 weights of 32,000 and that of the xylanase of pI 5.5 was 26,000. The optimal reaction temperature was 65–70° for the former enzymes and 50° 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.