P. Devos, H. Hers
Aug 1, 1979
Citations
0
Influential Citations
66
Citations
Journal
European journal of biochemistry
Abstract
When fasted rats or mice were refed, liver glycogen was synthesised at a linear rate of approximately 1 %/h for a period of about 6 h. The administration of a radioactive precursor, usually ['4C]galactose, allowed pulse labelling of the glycogen formed at various times after the initiation of refeeding. Soon after the administration of the label, the radioactive glucosyl units were preferentially located on the outer chains of glycogen. An almost equal distribution between the inner and outer chains was attained after a time which increased with increasing amounts of preexisting glycogen. Later on, the radioactive molecules were not further enlarged although the mass of glycogen increased threefold. The degradation of the glycogen that had been labelled at various times after initiation of refeeding was induced either in vivo in anesthetized rats, or in vitro in isolated hepatocytes and in a cell-free system made up of the enzyme-glycogen complex as isolated by concanavalin A. Under all of these conditions, the radioactive units that were incorporated last were liberated first and vice versa. This ordered degradation could not be explained by the initial removal of outer chains. In the concanavalin-A-bound glycogen, the ordered degradation was much less apparent when the preparation had been submitted to high-speed centrifugation, vigorous homogenization, ultrasonic treatment or exposure to detergents. In the mammalian liver, glycogen is present in the form of rosettes the diameter of which approximates 0.1 pm [I]. These large structures have also been called alpha-particulate glycogen and are made up of subunits termed beta particles [2]. The beta subunits are similar in size (diameter 15-30 nm) and general appearance to the particles of glycogen seen in muscle and in most other mammalian cells; they presumably correspond to the branched structure, made of inner and outer chains, which is currently considered as a glycogen molecule. Calculations based on the dimension of the particles and on the density of glycogen allowed a very rough estimation of the molecular weight ; they yielded values of the order of 4 x lo6 for the beta subunit and of 400 x lo6 for the alpha particles [3]. Ultracentrifugal studies [4- 61 have given very divergent values and have indicated the presence of a small percentage of extremely large structures the mass of which could be several times that of an alpha particle. It is not known at the present time whether or not the beta subunits are