Some characteristics of beta-D-xylopyranosidases, alpha-L-arabinofuranosidases and an arabinoxylan alpha-L-arabinofuranohydrolasefrom wheat bran and germinated wheat

Enzymes from wheat bran and germinated wheat involved in the degradation of arabinoxylan and arabinoxylooligosaccharides were investigated. Four p-nitrophenyl-alpha-L-arabinofuranoside hydrolysing activities (ArafI-IV) and three p-nitrophenyl-beta-D-xylopyranoside hydrolysing activities (XylpI-III) were identified in wheat kernels and germinating wheat. Two of these activities, ArafI and XylpII, were purified about 10 000-fold from wheat bran. Both enzymes were inactive towards polymeric arabinoxylan. ArafI produced no arabinose but some xylose from arabinoxylooligosaccharides, 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 towards 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 the third and fifth day, after which some of them decreased again by the seventh day. ArafI-IV were inhibited strongly by arabinonic acid-gamma-lactone, while xylonic acid-gamma-lactone was a good inhibitor of XylpI-III. The latter lactone also inhibited ArafI. Neither of these lactones inhibited AXH. Endoxylanase activity was demonstrated but not quantified. (C) 1996 Academic Press Limited