SOME CHARACTERISTICS OF BETA-D-XYLOPYRANOSIDASES, ALPHA-L-ARABINOFURANOSIDASES AND AN ARABINOXYLAN ALPHA-L-ARABINOFURANOHYDROLASEFROM WHEATBRAN AND GERMINATED WHEAT

Enzymes from wheat bran and germinated wheat involved in the degradati on of arabinoxylan and arabinoxylooligosaccharides were investigated. Four p-nitrophenyl-alpha-L-arabinofuranoside hydrolysing activities (A rafI-IV) and three p-nitrophenyl-beta-D-xylopyranoside hydrolysing act ivities (XylpI-III) were identified in wheat kernels and germinating w heat. Two of these activities, ArafI and XylpII, were purified about 1 0 000-fold from wheat bran. Both enzymes were inactive towards polymer ic arabinoxylan. ArafI produced no arabinose but some xylose from arab inoxylooligosaccharides, while XylpII gave only xylose upon incubation with this substrate. An arabinoxylan arabinofuranohydrolase (AXH) was found in wheat bran and germinated wheat. This enzyme was active towa rds the polymeric substrate, but was unable to hydrolyse p-nitrophenyl -alpha-L-arabinofuranoside. The M(r)s of these enzymes were determined by size exclusion chromatography and were in the range of 40-50 000, except for ArafIII, for which a M(r) of 104 000 was determined. During germination, the levels of these enzymes increased markedly between t he third and fifth day, after which some of them decreased again by th e seventh day. ArafI-IV were inhibited strongly by arabinonic acid-gam ma-lactone, while xylonic acid-gamma-lactone was a good inhibitor of X ylpI-III. The latter lactone also inhibited ArafI. Neither of these la ctones inhibited AXH. Endoxylanase activity was demonstrated but not q uantified. (C) 1996 Academic Press Limited