THE STRUCTURE OF GLYCOGENS

Summary 1. The usual criteria for identification of glycogen are discussed. It is pointed out that these can be applied equally well to amylopectin and α‐amylodextrin. Numerous so‐called glycogens in plants and micro‐organisms may not be chemically identical with animal glycogens, which may quite well vary among themselves. 2. Mention is made of the methods of isolation and purification. It is considered that precipitation by acetic acid gives the purest material in that nitrogen and phosphate can be eliminated, in many cases entirely. 3. The limitations of the end‐group assay are discussed. This method reveals the sole fact that all glycogens are built up from ‘unit chains’, but gives no information as to the detailed structure of these chains. It is, therefore, not possible to say whether glycogens from different sources are chemically the same or not. 4. A description is given of the difficulties in attempting to analyse glycogens from the aspect of determining the nature of the linkage uniting the unit chains. The suggestion is made that information to this end will have to be obtained by use of stepwise enzymic degradation of the polysaccharide. 5. The latest work on molecular weights is summarized. There is considerable variation according to the type of source from which the glycogen has been isolated. This work is the first indication that there are at least physical differences between glycogens.