TAXI type endoxylanase inhibitors in different cereals.

An affinity-based purification procedure with the immobilized family 11 Bacillus subtilis endoxylanase XynA allowed us to obtain high yields of highly pure endoxylanase inhibitor fractions from rye, barley, and durum wheat. In contrast, no inhibitors interacting with the B. subtilis endoxylanase affinity column are present in corn, buckwheat, rice, and oats. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis and inhibitor specificity showed that the isolated inhibitors belonged to the TAXI endoxylanase inhibitor family, thus providing a view on the diversity of this cereal inhibitor family. The isolated inhibitors are basic proteins of ca. 40 kDa, occurring in two molecular forms, with pI values of ca. 8.5 (durum wheat) and ca. 9.0 (rye, barley). They are, in general, strong inhibitors of family 11 endoxylanases but not of family 10 endoxylanases. Because cereal endogenous endoxylanases belong to the latter family, this probably indicates that they do not influence cereal metabolic processes. For the first time, endoxylanase inhibitors, similar to TAXI I and TAXI II from wheat, were isolated from durum wheat and characterized. For each cereal, high-resolution cation exchange chromatography revealed the presence of multiple isoinhibitors, each of which occurs in two molecular forms. However, in durum wheat and barley, a single isoform is predominantly present.