The helical structure of the β -1, 3-linked xylan in some siphoneous green algae

Abstract

An account is given of the conformation of a β -1, 3-linked xylan which is the structural poly-saccharide in some siphoneous green algae. The cell walls from Penicillus dumetosus were studied by X -ray diffraction, infra-red absorption and model building. The structure consists of three xylan polymer chains intertwining to form a three-strand helix with symmetry sr. Each helix has six xylose residues per turn in a pitch of approximately 18 Å. A novel type of inter-chain bonding has been proposed which consists of a cyclic triad of hydrogen bonds formed between the O 2 atoms, one from each individual chain. Computations show that the molecules are in fixed orientation in a hexagonal lattice. The calculations favour right-handed helices and there is evidence of stoichiometrically bound water on the surface of the molecule.