Endogeneous β-d-xylosidase and α-l-arabinofuranosidase activity in flax seed mucilage

Abstract

Flax seed mucilage (FM) contains a mixture of highly doubly substituted arabinoxylan as well as rhamnogalacturonan I with unusual side group substitutions. Treatment of FM with a GH11 Bacillus subtilis XynA endo 1,4-β-xylanase (BsX) gave limited formation of reducing ends but when BsX and FM were incubated together on different wheat arabinoxylan substrates and birchwood xylan, significant amounts of xylose were released. Moreover, arabinose was released from both water-extractable and water-unextractable wheat arabinoxylan. Since no xylose or arabinose was released by BsX addition alone on these substrates, nor without FM or BsX addition, the results indicate the presence of endogenous β-D: -xylosidase and α-L: -arabinofuranosidase activities in FM. FM also exhibited activity on both p-nitrophenyl α-L: -arabinofuranoside (pNPA) and p-nitrophenyl β-D: -xylopyranoside (pNPX). Based on K ( M ) values, the FM enzyme activities had a higher affinity for pNPX (K ( M ) 2mM) than for pNPA (K ( M ) 20mM).