PLANT PHYSIOLOGY , Vol 115, Issue 4 1619-1627, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Identification and Characterization of a Novel Arabinoxylanase from Wheat Flour
G. Cleemput, K. Van Laere, M. Hessing, F. Van Leuven, S. Torrekens and J. A. Delcour
Katholieke Universiteit Leuven, Laboratorium voor Levensmiddelenchemie, Kardinaal Mercierlaan 92, B-3001 Heverlee, Belgium (G.C., K.V.L., J.A.D.)
An endogenous wheat (Triticum aestivum) flour endoxylanase was purified to
homogeneity from a crude wheat flour extract by ammonium sulfate
precipitation and cation-exchange chromatography. The 30-kD protein had an
isoelectric point of 9.3 or higher. A sequence of 19 amino acids at the NH2
terminus showed 84.2% identity with an internal sequence of the 15-kD
grain-softness protein, friabilin. High-performance anion-exchange
chromatography and gel-permeation analysis of the hydrolysis products
indicated the preferential hydrolysis of highly branched structures by the
enzyme; wheat arabinoxylan and rye (Secale cereale) arabinoxylan (high
arabinose to xylose ratios) were hydrolyzed more efficiently by this enzyme
than oat (Avena sativa) spelt xylan (low arabinose to xylose ratios). The
release of the hydrolysis products as a function of time suggested that the
endoxylanolytic activity was associated with the release of arabinose units
from the polysaccharides, suggesting that the enzyme action is similar to
that by endoxylanases from Ceratocystis paradoxa, Aspergillus niger, and
Neurospora crassa. Although the enzyme released arabinose from
arabinoxylan, it did not hydrolyze
p-nitrophenyl-[alpha]-L-arabinofuranoside. From the above, it follows that
the enzyme, called arabinoxylanase, differs from most microbial
endoxylanases and from an endoxylanase purified earlier from wheat flour.