CHEMICAL STRUCTURE OF INSOLUBLE HYPHAL WALL GLUCAN OF PHYTOPHTHORA CINNAMOMI

The major component of hyphal walls of Phytophthora cinnamomi is an extremely insoluble, noncellulosic glucan. This is the residual polysaccharide left after removal of cellulose by exhaustive extraction of the walls with Schweizer's reagent. The structure of this noncellulosic glucan was investigated by methylation and periodate oxidation. Hydrolysis of the methylated glucan yielded the following amounts of O-methyl-D-glucoses: 2,3,4,6-tetra-O-methyl-D-glucose (15.4 mole %), 2,4,6-(plus some 2,3,6-) tri-O-methy-Dglucose (58.6 mole %), 2,4,-di-O-methyl-D-glucose (20.7 mole %), and 4,6-di-O-methyl-D-glucose (5.2 mole %). The structural significance of the last compound remains uncertain. The glucan consumed 0.41 mole of periodate and produced 0.16 mole of formic acid per mole of anhydroglucose unit. Reduction and hydrolysis of the periodate-oxidized glucan afforded glycerol, erythritol, and glucose in a molar ratio of 23:10:66. The results indicate that the insoluble hyphal wall glucan is a highly branched polysaccharide composed predominantly of β-1→3-linked glucose chains, with about four chain residues per branching point. Glucose residues connected by β links through both C-3 and C-6 serve as branching points. In addition, about 10% of the glucose units appeared joined by 1→4 linkages; these could correspond to cellulose chains firmly bound to the noncellulosic portion of the insoluble hyphal wall glucan. The possibility was expressed that the noncellulosic glucan of P. cinnamomi hyphal walls may be structurally similar to the insoluble cell wall (yeast) glucan of Saccharomyces cerevisiae. © 1969, American Chemical Society. All rights reserved.