The location of tetrasaccharide units in pullulan

The structure of pullulan, the extracellular a-d-glucan elaborated by the yeast-like fungus Aureobasidium pullulans, may be described as a polymaltotriose, the trisaccharides being linked by (1?6)-a-d-glucosidic bonds on the terminal d-glucosyl residues. Depending on the strain of the organism used, up to 6% of the trisaccharide units are replaced by maltotetraosyl residues. Exploiting the susceptibility of these tetrasaccharides to hydrolysis catalysed by porcine alpha-amylase, pullulan has been cleaved at these points and the fragments have been fractionated by gel-permeation chromatography. The heterogeneous size of the fragments indicates that there is no apparent, regular distribution of maltotetraosyl residues throughout the glucan. © 1983.