RESUMO
Two different endo-1,4-beta-xylanases, designated XA-1 and XA-2, and one beta-xylosidase (XD-1) have been purified by column chromatography to apparent homogeneity from the extracellular culture fluid of Phlebia radiata grown on wheat bran. The molecular masses of XA- 1, XA-2 and XD-1 were 18.6, 15.8 kDa, and 27 kDa, respectively. The isoelectric points for the xylanases were 6.7 and 4.1 and for the xylosidase - 5.9. The Km and Vmax values with larchwood xylan as substrate were 4.86 mg ml(-1) and 0.17 micromol min(-1) mg(-1) for XA-1; 2.7 mg ml(-1) and 3.91 micromol min(-1) mg(-1) for XA-2, whereas with pNPK as a substrate the Km and Vmax for XD-1 was 1.28 mM and 7.41 micromol min(-1) mg(-1). All the above enzymes are glycoproteins and the carbohydrate contents are for- XA-1 and XA-2 (6.70%, 3.58%) and for XD-1 (12.8%). Endoxylanase XA-1 and XA-2 were not able to release arabinose from rye arabinoxylan and birch xylan. Both enzymes were endo-acting, as revealed by their hydrolysis product profiles on xylan substrates.
