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Increases in glycogenin and glycogenin mRNA accompany glycogen resynthesis in human skeletal muscle

Increases in glycogenin and glycogenin mRNA accompany glycogen resynthesis in human skeletal muscle Glycogenin is the self-glycosylating protein primer that initiates glycogen granule formation. To examine the role of this protein during glycogen resynthesis, eight male subjects exercised to exhaustion on a cycle ergometer at 75% O 2 max followed by five 30-s sprints at maximal capacity to further deplete glycogen stores. During recovery, carbohydrate (75 g/h) was supplied to promote rapid glycogen repletion, and muscle biopsies were obtained from the vastus lateralis at 0, 30, 120, and 300 min postexercise. At time 0 , no free (deglycosylated) glycogenin was detected in muscle, indicating that all glycogenin was complexed to carbohydrate. Glycogenin activity, a measure of the glycosylating ability of the protein, increased at 30 min and remained elevated for the remainder of the study. Quantitative RT-PCR showed elevated glycogenin mRNA at 120 min followed by increases in protein levels at 300 min. Glycogenin specific activity (glycogenin activity/relative protein content) was also elevated at 120 min. Proglycogen increased at all time points, with the highest rate of resynthesis occurring between 0 and 30 min. In comparison, macroglycogen levels did not significantly increase until 300 min postexercise. Together, these results show that, during recovery from prolonged exhaustive exercise, glycogenin mRNA and protein content and activity increase in muscle. This may facilitate rapid glycogen resynthesis by providing the glycogenin backbone of proglycogen, the major component of glycogen synthesized in early recovery. granule; proglycogen; macroglycogen; recovery; carbohydrate Address for reprint requests and other correspondence: J. Shearer, Faculty of Medicine, Univ. of Calgary, Rm. 2502, 3330 Hospital Dr. NW, Calgary T2N 4N1, Canada (e-mail: jshearer@ucalgary.ca ) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png AJP - Endocrinology and Metabolism The American Physiological Society

Increases in glycogenin and glycogenin mRNA accompany glycogen resynthesis in human skeletal muscle

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References (35)

Publisher
The American Physiological Society
Copyright
Copyright © 2011 the American Physiological Society
ISSN
0193-1849
eISSN
1522-1555
DOI
10.1152/ajpendo.00100.2005
pmid
15870102
Publisher site
See Article on Publisher Site

Abstract

Glycogenin is the self-glycosylating protein primer that initiates glycogen granule formation. To examine the role of this protein during glycogen resynthesis, eight male subjects exercised to exhaustion on a cycle ergometer at 75% O 2 max followed by five 30-s sprints at maximal capacity to further deplete glycogen stores. During recovery, carbohydrate (75 g/h) was supplied to promote rapid glycogen repletion, and muscle biopsies were obtained from the vastus lateralis at 0, 30, 120, and 300 min postexercise. At time 0 , no free (deglycosylated) glycogenin was detected in muscle, indicating that all glycogenin was complexed to carbohydrate. Glycogenin activity, a measure of the glycosylating ability of the protein, increased at 30 min and remained elevated for the remainder of the study. Quantitative RT-PCR showed elevated glycogenin mRNA at 120 min followed by increases in protein levels at 300 min. Glycogenin specific activity (glycogenin activity/relative protein content) was also elevated at 120 min. Proglycogen increased at all time points, with the highest rate of resynthesis occurring between 0 and 30 min. In comparison, macroglycogen levels did not significantly increase until 300 min postexercise. Together, these results show that, during recovery from prolonged exhaustive exercise, glycogenin mRNA and protein content and activity increase in muscle. This may facilitate rapid glycogen resynthesis by providing the glycogenin backbone of proglycogen, the major component of glycogen synthesized in early recovery. granule; proglycogen; macroglycogen; recovery; carbohydrate Address for reprint requests and other correspondence: J. Shearer, Faculty of Medicine, Univ. of Calgary, Rm. 2502, 3330 Hospital Dr. NW, Calgary T2N 4N1, Canada (e-mail: jshearer@ucalgary.ca )

Journal

AJP - Endocrinology and MetabolismThe American Physiological Society

Published: Sep 1, 2005

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