Glycogenin activity in human skeletal muscle is proportional to
muscle glycogen concentration..
Shearer, J., I. Marchand, P. Sathasivam, M. A. Tarnopolsky, T. E.
Graham.
1Department of Human Biology and Nutritional Sciences, University
of Guelph, Guelph, Ontario. Canada. N1G 2W1 and 2Department of
Medicine and Kinesiology, McMaster University. Hamilton, Ontario.
Canada. L8N 3Z5
APStracts 6:0222E, 1999.
The de novo biosynthesis of glycogen is catalyzed by glycogenin, a
self-glucosylating protein primer. To date, the role of glycogenin in
regulating glycogen metabolism and the attainment of maximal glycogen
levels in skeletal muscle is unknown. We measured glycogenin activity
following enzymatic removal of glucose by (-amylase; an indirect
measure of glycogenin amount. Seven male subjects performed an
exercise and dietary protocol which resulted in one high carbohydrate
leg (HL) and one low carbohydrate leg (LL) prior to testing. Resting
muscle biopsies were obtained and analyzed for total glycogen,
proglycogen (PG), macroglycogen (MG), and glycogenin activity.
Results showed differences (p<0.05) between HL and LL for total
glycogen (438.0 +/- 69.5 vs. 305.7 +/- 57.4 mmol glucosyl units kg-1
dw) and PG (311.4 +/- 38.1 vs. 227.3 +/- 33.1 mmol glucosyl units kg
-1 dw). A positive correlation between total muscle glycogen content
and glycogenin activity (r = 0.84, p<0.001) was observed. Similar
positive correlations (p<0.05) were also evident between both PG
and MG concentration and glycogenin activity (PG; r = 82, MG; r =
0.84). It can be concluded that glycogenin does display activity in
human skeletal muscle and is proportional to glycogen concentration.
Thus, it must be considered as a potential regulator of glycogen
synthesis in human skeletal muscle.
Received 10 May 1999; accepted in final form 20 September 1999.
APS Manuscript Number E226-9.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 8 October 1999