IDENTIFICATION AND CHARACTERIZATION OF A NOVEL ARABINOXYLANASE FROM WHEAT-FLOUR

An endogenous wheat (Triticum aestivum) flour endoxylanase was purifie d to homogeneity from a crude wheat flour extract by ammonium sulfate precipitation and cation-exchange chromatography. The 30-kD protein ha d 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-e xchange chromatography and gel-permeation analysis of the hydrolysis p roducts indicated the preferential hydrolysis of highly branched struc tures by the enzyme; wheat arabinoxylan and rye (Secale cereale) arabi noxylan (high arabinose to xylose ratios) were hydrolyzed more efficie ntly by this enzyme than oat (Avena sativa) spelt xylan (low arabinose to xylose ratios). The release of the hydrolysis products as a functi on of time suggested that the endoxylanolytic activity was associated with the release of arabinose units from the polysaccharides, suggesti ng that the enzyme action is similar to that by endoxylanases from Cer atocystis 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 t hat the enzyme, called arabinoxylanase, differs from most microbial en doxylanases and from an endoxylanase purified earlier from wheat flour .