Differential glucose incorporation into glycogen by Hymenolepis diminuta.

1. A differential incorporation of 14C-glucose into two distinct molecular weight fractions of glycogen from the tapeworm Hymenolepis diminuta has been observed. Changes in these labeling patterns as a function of the glycogen level have been examined. 2. After incubation of Hymenolepis diminuta in media containing 14C-glucose under steady state conditions of glycogen metabolism, the specific activity of the high molecular weight fraction was significantly greater than that of the low molecular weight fraction. This difference was due to an almost 3fold greater specific activity in the phosphorylase limit dextrin of the high molecular weight fraction. 3. By contrast, upon reduction of the glycogen level from 8% to approximately 1.5 % and subsequent resynthesis of glycogen from 14C-glucose, the specific activity of the high molecular weight fraction was much lower than that of the low molecular weight fraction. 4. The relative rates of incorporation of 14C-glucose into glycogen as a function of the initial glycogen level were determined. 5. In any given glycogen sample, regardless of the glycogen level, the high and low molecular weight fractions had identical outer chain lengths and the same degree of branching. 6. The results obtained establish significant metabolic differences between the high and low molecular weight glycogen fractions.