Substrate Specificity of the α-L-arabinofuranosidase from Trichoderma reesei

The precise substrate specificities of an alpha-L-arabinofuranosidase from Trichoderma reesei were investigated. The enzyme released arabinose at appreciable rates from p-nitrophenyl-alpha-L-arabinofuranoside, O-alpha-L-arabinofuranosyl-(1 --> 3)-O-beta-D-xylopyranosyl-(1 --> 4)-D-xylopyranose (A(1)X(2)), arabinan, arabinoxylan, arabinogalactan, debranched-arabinan and gum arabic, but not from O-beta-D-xylopyranosyl-(1 --> 4)-[O-alpha-L-arabinofuranosyl-(1 --> 3)]-O-beta-D-xylopyranosyl-(1 --> 4)-D-xylopyranose (A(1)X(3)) or O-beta-D-xylopyranosyl-(1 --> 2)-O-alpha-L-arabinofuranosyl(1 --> 4)-O-beta-D-xylopyranosyl-(1 --> 4)-O-beta-D-xylopyranosyl-(1 --> 4)-D-xylopyranose (A(1)X(4)). The enzyme hydrolyzed methyl 2-O-, methyl 3-O- and methyl 5-O-alpha-L-arabinofuranosyl-alpha-L-arabinofuranosides furanosides to arabinose and methyl alpha-L-arabinofuranoside with the order of hydrolysis being: (1 --> 5)->(1 --> 2)-greater than or equal to(1 --> 3)-linkages. The enzyme hydrolyzed the (1 --> 3)-linkage faster than the (1 --> 5)linkage of methyl 3,5-di-O-alpha-L-arabinofuranosyl-alpha-L-arabinofuranoside. The degree of conversion of arabinan and debranched-arabinan to monosaccharides by the enzyme was 33.0% and 9.1%, respectively. The alpha-L-arabinofuranosidase preferentially cleaved the arabinosyl sidechain from the arabinan rather than the terminal arabinosyl residue of the arabinan backbone.