THE STRUCTURE OF LICHENIN: SELECTIVE ENZYMOLYSIS STUDIES

Abstract

Lichenin, the poly-[beta]-D-glucan of Cetraria islandica (Iceland moss), is found by enzymic degradation to differ in fine structure from the poly-[beta]-D-glucans of cereal grains. Enzymolysis has been carried out with a celluloase and a laminarinase preparation, the former yielding mainly O-[beta]-D-glucopyranosyl-(1[forward arrow]3)-O-[beta]-D-glucopyranosyl-(1[forward arrow]4)-[alpha]-D-glucose, and the latter mainly O-[beta]-D-glucopyranosyl-(1[forward arrow]4)-O-[beta]-D-glucopyranosyl-(1[forward arrow]3)-[alpha]-D-glucose. Di- and tetra-saccharides are produced in small proportions. Steric aspects of these enzymic degradations are discussed. The basis constitution of lichenin is represented by a tetrameric unit in which two adjacent (1[forward arrow]4) linkages alternate with an isolated (1[forward arrow]3) linkage; occasionally four consecutive monomers are linked by (1[forward arrow]4) bonds. The glucans of cereal origin differ mainly in possessing a higher proportion of the latter structural sequence. Despite their close chemical similarity to cellulose, all of these glucans are soluble, a property that appears to be related to the even distribution of [beta]-(1[forward arrow]3) bonds along the chains, with a resulting disruption of linear orientation effects.