Elucidation of the Fine Structure of Oyster Glycogen

Abstract

Glycogen, a reserve polysaccharide of animals and microorganism, has a highly branched structrue, consisting of α-(1-4) linked D-glucose resides some of which are branched at O-6 position. Although hitherto conducted extensive studies showed, unlike amylopectin, glycogen is present usually as a spherical molecules in the tissues of living organisms, its fine structural feature has not fully been elucidated. In the present study, the fine structure of multiple-branched oyster glycogen has been elucidated by successive peeling of the spherical molecule by using the actions of β-amylase followed by pullulanase. The oyster glycogen, purified by extration with dimethyl sulfoxide, had molecule weight, 4x10⁵ (hplc). Methylation analysis and also gel-filtration after isoamylase-debranching revealed that it has CL, approx. 12. De branching with pullulanase indicated that, average length of (1→4 )-unit is 6-9,corresponding to the length of A-chains, which consist q equal numbers of odd and even number of the glucosyl residues. Four times successive actions with β-amylase and pullulanase (to remove G2 -G3 glycosyl units originating from A-chains), yieled the corresponding degraded glycogen (stub-free β-dextrins). Comparison of the chain length and β-amylolysis limit in each step, indicated that the glycogen has truly multiple-branched structure, and the core portion of the chain length (I. C.) of 1.8-2.0, to form a compact spherical molecule. In addition, it may be noteworthy that the oyster glycogen may contain a small but significant proportion (ca. 2%) of peptide, consisting of taurine and other amino acids.