SELECTIVE ENZYMOLYSIS OF POLY-β-D-GLUCANS, AND THE STRUCTURE OF THE POLYMERS

The soluble poly-β-D-glucan from oats has been subjected to degradation by two different types of enzymes. "Cellulase" converts the polysaccharide to a trisaccharide, 4-O-β-D-lamina-ribiosyl-D-glucose, and two tetrasaccharides, 3′-O-β-D-cellobiosyl-D-cellobiose and 4′-O-β-D-laminaribiosyl-D-cellobiose. Degradation by the second enzyme, "laminarinase", produces a trisaccharide, 3-O-β-D-cellobiosyl-D-glucose, and a tetrasaccharide, 3-O-β-D-cellotriosyl-D-glucose. These products, which account for 75-85% of the polymer in each experiment, have been characterized by chemical methods. The data show that the glucan is composed almost entirely of two types of structural sequences: one is a tetrameric unit in which a single β-(1 → 3) linkage alternates with two β-(1 → 4) linkages, and the other, a pentameric unit in which a single β-(1 → 3) linkage alternates with three consecutive β-(1 → 4) linkages.The soluble poly-β-D-glucan from barley has been shown by enzymolysis with the "cellulase" to be closely related in detailed structure to the oat polymer.Steric aspects of the enzymic degradations are discussed.