Glycogen and amylopectin are related polysaccharides in that they are homopolymers of a-glucose containing 1 + 4-and 1 + 6-linkages. They are both branched structures consisting of linear chains of glucose units linked 1+ 4 which are joined by l+ 6-linkages at the branch points (Fig. 1). A characteristic of these structures is their average chain length, which is in the range of 10 to 16 for glycogen and 20 to 24 for amylopectins (1,2). The average chain length may be defined as the average number of glucose units in an uninterrupted sequence of 1 + 4bonds. Methods for the determination of average chain length revolve around the determination of the number of chain-ends, i.e., of end-group analysis. Reference to Fig. 1 shows that there are two types of end-group, the nonreducing end group and the glucosyl end involved in the 1 + 6linkage which becomes the reducing end on hydrolysis of that bond. Of the end-group methods so far developed for glycogen and amylopectin, chemical methods, e.g., methylation (3) and periodate oxidation (4), determine the nonreducing end group. Enzymic methods determine the potential reducing end. The two enzymic methods most widely used both rely on the use of two enzymes, the first an exoenzyme specific for the hydrolysis of the 1 -+ 4-linkages, the second a debranching enzyme specific for the 1 + 6-linkage. The reducing end glucose unit is released as free glucose, distinct from the other segments of the chain.
The first method, that of Gori and Larner (5), utilizes rabbit muscle phosphorylaee and the rabbit muscle debranching enzyme system. The latter, amylo-l,&glucosidase/oligo-1,4+
1,4-glucantransferase,l is composed of two enzymic activities which are both essential for the debranching process and which are associated with a single protein (6,7). Cori and Larner demonstrated that phosphorylase a.nd their preparation of debranching enzyme caused the conversion of glycogen and amylol Abbreviated to glucosidase-transferase in the rest of the text.