Glycogen Turnover 



297 



Fig. 2. Distribution of radioactivity in liver and carcass glycogen between 



periphery and limit dextrin. The total counts per minute in the maltose and in 



the limit dextrin (glycogen, j3-amylase) have been determined in each sample of 



glycogen after exhaustive treatment with /3-amylase. 



erally in the glycogen molecule, it is these glucosidic residues rather 

 than circulating glucose which give rise to the glucosidic residues situ- 

 ated in the central core of the molecule. This relationship between 

 precursors and products may be expressed by the sequence: 



Circulating glucose — » Glucosidic residues at periphery of glycogen — > 

 Glucosidic residues at center of glycogen 



It is interesting to compare the distribution of radioactivity within 

 the molecule of liver glycogen derived from the fasted and from the 

 fed rat. The experiments recorded in Table 2 represent such a com- 

 parison. One rat was fasted for 24 hours prior to glucose-C 14 injection ; 

 another had continuous access to diet. Three hours after injection each 

 rat was killed, and the distribution of isotope within glycogen was 

 studied. The striking finding was that, whereas in the liver from the 

 fed rat the major portion of the label was in the periphery (maltose) 

 of the glycogen, the glycogen recovered from the liver of the fasted 



