Interbranch Sequences in the Wheat Arabino-Xylan: Selective Enzymolysis Studies

A Streptomyces xylanase degrades the soluble arabino-xylan of wheat with formation of polymeric fragments and several oligosaccharides. The overall data, together with information about the spatial requirements of the xylanase, show that (a) the arabino-xylan molecules are constituted predominantly of highly branched regions in which isolated and paired L-arabinosyl branches are separated by single D-xylosyl units; (b) at unequal intervals (averaging 20−25 main-chain units) this type of sequence is interrupted by "open regions" of at least two to five unbranched D-xylosyl units; and (c) infrequently, an L-arabinosyl branch is removed from other branches at either side by at least two D-xylosyl units.A new tetrasaccharide isolated from the enzymic digest is shown to be O-α-L-arabino-furanosyl-(1 → 3)-O-[β-D-xylopyranosyl-(1 → 4)]-O-β-D-xylopyranosyl-(1 → 4)-D-xylose.