Overexpression of glycogen synthase in mouse muscle results in less branched glycogen.
Glycogen, a branched polymer of glucose, serves as an energy reserve in many organisms. The degree of branching likely reflects the balance between the activities of glycogen synthase and branching enzyme. Mice overexpressing constitutively active glycogen synthase in skeletal muscle (GSL30) have elevated muscle glycogen. To test whether excess glycogen synthase activity affected glycogen branching, we examined the glycogen from skeletal muscle of GSL30 mice. The absorption spectrum of muscle glycogen determined in the presence of iodine was shifted to higher wavelengths in the GSL30 animals, consistent with a decrease in the degree of branching. As judged by Western blotting, the levels of glycogenin and the branching enzyme were also elevated. Branching enzyme activity also increased approximately threefold. However, this compared with an increase in glycogen synthase of some 50-fold, so that the increase in branching enzyme in response to overexpression of glycogen synthase was insufficient to synthesize normally branched glycogen.
Pederson
Bartholomew A
BA
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, and Indiana University Center for Diabetes Research, Indianapolis, IN 46202-5122, USA.
Csitkovits
Anna G
AG
Simon
Renee
R
Schroeder
Jill M
JM
Wang
Wei
W
Skurat
Alexander V
AV
Roach
Peter J
PJ
D015061:1,4-alpha-Glucan Branching Enzyme / Q000378:metabolism; D000818:Animals; D005964:Glucosyltransferases; D006003:Glycogen / Q000096:biosynthesis* / Q000737:chemistry*; D006006:Glycogen Synthase / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D051379:Mice; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000378:metabolism; D009154:Mutation
D006023:Glycoproteins; C051887:glycogenin; D006003:Glycogen; D005964:Glucosyltransferases; D006006:Glycogen Synthase; D015061:1,4-alpha-Glucan Branching Enzyme