THE BETA-D-XYLOSIDASE OF TRICHODERMA-REESEI IS A MULTIFUNCTIONAL BETA-D-XYLAN XYLOHYDROLASE

An extracellular multifunctional beta-D-xylan xylohydrolase, previousl y described as beta-xylosidase, was purified from Trichoderma reesei R UT C-30 to physical homogeneity. The active enzyme was a 100 (+/-5) kD a glycosylated monomer that exhibited a pI of 4.7. Its activity was op timal at pH 4 and it was stable between pH 3 and 6. Its temperature-st ability was moderate (70% of activity remaining after 60 min at 50 deg rees C) and optimal activity was observed at 60 degrees C. It is capab le of hydrolysing beta-1,4-xylooligosaccharides [degree of polymerizat ion (DP) 2-7], the apparent V-max increasing with increasing chain len gth. The enzyme also attacked debranched beech-wood (Lenzing) xylan an d 4-O-methylglucuronoxylan, forming xylose as the only end product. Th e K-m for xylan was 0.7 g/l. For this reason we consider the enzyme to be a beta-D-xylan xylohydrolase. The enzyme also exhibits alpha-L-ara binofuranosidase activity on 4-nitrophenyl alpha-L-arabinofuranoside, and evidence is presented that this is not caused by an impurity in th e enzyme preparation. The beta-D-xylan xylohydrolase exhibits glycosyl transferase activity with xylooligosaccharides and at high concentrati ons of 4-nitrophenyl beta-D-xylopyranoside (4-Nph-beta-Xyl). The enzym e hydrolyses beta-1, 4-linkages preferentially to beta-1,3-linkages, a nd beta-1,2-linked xylo-oligosaccharides are not hydrolysed at all. Th e enzyme liberates terminal beta-1,4-xylopyranose residues linked to a 2-O-substituted xylopyranose residue, but not that linked to a 3-O-su bstituted xylopyranose residue. The enzyme does not attack methyl, met hyl 1-thio-, benzyl or butyl 1-thio-beta-D-xylopyranosides and 4-napht hyl, 2-naphthyl and phenyl beta-D-xylopyranosides.