A protein-bound glycogen component of rat liver

It has long been claimed, but frequently disputed, that part of the glycogen in rat liver is insoluble in 10% trichloroacetic acid, and a physiological significance was ascribed to the existence of the two pools of glycogen, desmo-glycogen, the insoluble form, and lyo-glycogen, the soluble component. Desmo-glycogen was thought to owe its acid insolubility to a covalent binding to protein. Recent claims that glycogen, similarly insoluble in acid, can be synthesized in vitro have renewed the interest in desmo-glycogen. We have obtained trichloroacetic acid-insoluble glycogen from rat liver and find that, despite subjecting the glycogen to proteolysis, peptide material remains in close association with the glycogen through a number of purification procedures and is freed from glycogen only by enzymic decomposition of the latter. The tenacity with which the glycogen and peptide material remain in association with each other is suggestive of the occurrence of protein-bound glycogen.