Purification and characterization of three (1----4)-beta-D-xylan endohydrolases from germinated barley.

Three (1----4)-beta-D-xylan xylanohydrolases (xylan endohydrolases, EC 3.2.1.8) have been purified 1200-2800-fold from extracts of germinated barley (Hordeum vulgare L. cv. Clipper) by a sequence of ammonium sulphate fractionation, Procion-blue-dye chromatography, ion-exchange and gel filtration chromatography. The enzymes are likely to function in the depolymerization of cell wall arabinoxylans during mobilization of the starchy endosperm. They are classified as endohydrolases on the basis of analyses of products released during hydrolysis of a (1----4)-beta-xylan. The three xylan endohydrolases are monomeric proteins of apparent Mr 41,000 and all have isoelectric points of 5.2. The sequences of the 30 NH2-terminal amino acids of the three enzymes are the same, but it is not yet known whether they represent the products of separate genes or originate by differences in post-translational modification of a single gene product.