The characterization of a chitin-associated D-glucan from the cell walls of Aspergillus niger

Abstract

Exhaustive extraction of the cell walls of Aspergillus niger with 10% NaOH solution leaves an alkali-resistant residue containing chitin and glucan as the major components. The glucan in this residue comprises 58.7% of the total cell wall glucan and was characterized by permethylation, and identification of the resulting O- methyl- D-glucoses obtained after hydrolysis by gas-liquid chromagtography and mass spectrometry of the derived partially acetylated, partially methylated, [1- 2H]alditols. The glucan was separated from the chitin by acetylation of the alkali-resistance material, a procedure which separates a large portion of the total glucan as a chloroformsoluble acetate, abd by treatment of the alkali-insoluble residue with nitrous acid, a procedure which was found to render the complex soluble in dimethylsulfoxide and amenable, therefore, to permethylation. The data collected suggests that the preparation is an essentially linear glucan containing 85–95% 1 → 3 linkages and 10–15% 1 → 4 linkages. An analysis of the glycosidic linkages using NMR spectroscopy indicate that both α and β linkages are present in the ratio of 4:1. An identical glucan appears to be present in the cell walls of Penicillium chrysogenum as well as the spore cell walls of both organisms, as evidenced by methylation studies.