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Triticum aestivum L. endoxylanase inhibitor (TAXI) consists of two proteins, TAXI I and TAXI II,
with different specificities. KURT GEBRUERS (1), Winok Debyser (1), Hans Goesaert (1), Paul
Proost (2), and Jan A. Delcour (1). (1) Laboratory of Food Chemistry, Katholieke Universiteit Leuven; (2)
Department of Microbiology and Immunology, Katholieke Universiteit Leuven.
The Triticum aestivum L. endoxylanase inhibitor (TAXI)
discovered by Debyser and Delcour (1997, Inhibitors of xylanolytic and beta-glucanolytic enzymes,
European patent filed April 1997, published as WO 98/49278) and Debyser and others (1997, J. Am. Soc.
Brew. Chem. 55, 153-156) is a mixture of two different endoxylanase inhibitors, called TAXI I and TAXI
II. By using A. niger as well as B. subtilis endoxylanases for assaying inhibition activity,
both inhibitors could be purified to homogeneity from wheat (Triticum aestivum L., var. Soissons).
TAXI I and TAXI II have similar molecular structures. They both have a molecular mass of ca. 40.0 kDa,
are not glycosylated and occur in two molecular forms, i.e. a non-proteolytically and a proteolytically
processed. However, the pI of TAXI II (at least 9.3) is higher than that of TAXI I (8.8). TAXI I and TAXI
II clearly show a different endo-beta-1,4-xylanase inhibition activity towards different endoxylanases. The
N-terminal amino acid sequences of both inhibitors show a high degree of identity, which may indicate that
there is an evolutionary relationship between them.
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