AJP - Endocrinology and Metabolism, Vol 253, Issue 4 E360-E369, Copyright © 1987 by American Physiological Society
Patterns of glycogen turnover in liver characterized by computer modeling
J. H. Youn and R. N. Bergman
Department of Physiology and Biophysics, University of Southern California Medical School, Los Angeles 90033.
We used a computer model of liver glycogen turnover to reexamine the data
of Devos and Hers, who reported the time course of accumulation in and loss
from glycogen of label originating in [1-14C]galactose injected at
different times after the start of refeeding of 40-h fasted mice or rats.
In the present study computer representation of individual glycogen
molecules was utilized to account for growth and degradation of glycogen
according to specific hypothetical patterns. Using this model we could
predict the accumulation and localization within glycogen of labeled
glucose residues and compare the predictions with the previously published
data. We considered three specific hypotheses of glycogen accumulation
during refeeding: 1) simultaneous, 2) sequential, and 3) accelerating
growth. Hypothetical patterns of glycogen degradation were 1) ordered and
2) random degradation. The pattern of glycogen synthesis consistent with
experimental data was a steadily increasing number of growing glycogen
molecules, whereas during degradation glycogen molecules are exposed to
degrading enzymes randomly, rather than in a specific reverse order of
synthesis. These patterns predict the existence of a specific mechanism for
the steadily increasing "seeding" of new glycogen molecules during
synthesis.
