D-XYLAN-DEGRADING ENZYME-SYSTEM FROM THE FUNGUS PHANEROCHAETE-CHRYSOSPORIUM - ISOLATION AND PARTIAL CHARACTERIZATION OF AN ALPHA-(4-O-METHYL)-D-GLUCURONIDASE

A number of fungi were screened for their capacities to produce extrac ellular alpha-(4-O-methyl)-D-glucuronidase. Of those tested, Phaneroch aete chrysosporium ATCC 24725 produced the enzyme in greatest yield. T he single alpha-(4-O-methyl)-D-glucuronidase produced by this fungus w as purified by a series of chromatographic methods involving anion exc hange, hydrophobic interaction and chromatofocusing. Isolated in this way, the enzyme had an apparent molecular mass of 112 kDa in sodium do decyl sulphate polyacrylamide gels, and a pi of 4.6 when determined by isoelectric focusing in polyacrylamide gels. The enzyme was optimally active at pH 3.5, but showed significant activity over the pH range 3 -5. In the absence of substrate the enzyme was inactivated at pH 3.5 i n 2 h at 50 degrees C: at pH 5.0 it retained 42% of its activity for 2 4 h at this temperature. The enzyme showed little activity on glucuron oxylan polysaccharides, but some short-chain xylo-oligosaccharides whi ch were substituted with a-linked 4-O-methyl-D-glucopyranosyl uronic a cid attached to the 2-position of the non-reducing D-xylopyranosyl res idue were readily hydrolysed. There were marked synergistic effects ap parent in the release of 4-O-methyl-D-glucopyranosyl uronic acid from various glucuronoxylans when the alpha-(4-O-methyl)-D-glucuronidase wa s acting in concert with endo-(1 --> 4)-beta-D-xylanase, and with beta -D-xylosidase and/or an alpha-L-arabinofuranosidase.