Glyconeogenic and glycogenic enzymes in chronically active and normal skeletal muscle.
The chronically active (pseudomyotonic) gastrocnemius muscle in the C57B16J dy2J/dy2J mouse contains both elevated lactate and glycogen as well as fibers that have high amounts of glycogen and enhanced glyconeogenic activity. In the present study we analyze the activities of some key glyconeogenic enzymes to assess the causes of elevated muscle glycogen and to determine the pathway for glycogen synthesis from lactate. Glycogen synthase, malate dehydrogenase, phosphoenolpyruvate carboxykinase, and malic enzyme were all elevated in homogenates of the chronically active muscle. Activities of glycogen phosphorylase and fructose 1,6-bisphosphatase were decreased in whole muscle homogenates. Histochemistry demonstrated that the high-glycogen fibers were typically fast-twitch glycolytic fibers that had high glycogen synthase, glycogen phosphorylase, and malic enzyme activities. Malate dehydrogenase activity followed succinate dehydrogenase activity and did not correlate to high-glycogen fibers. Thus the high-glycogen fibers have an elevated enzymatic capacity for glycogen synthesis from lactate, and the pathway may involve use of the pyruvate kinase bypass enzymes.
Department of Zoology and Physiology, Louisiana State University, Baton Rouge 70803.
R J
RJ
Talmadge
H
H
Silverman
D000818:Animals; D006003:Glycogen / Q000096:biosynthesis*; D006006:Glycogen Synthase / Q000378:metabolism; D006651:Histocytochemistry; D008291:Malate Dehydrogenase / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009132:Muscles / Q000201:enzymology / Q000378:metabolism*; D009137:Muscular Dystrophy, Animal / Q000201:enzymology / Q000378:metabolism; D009222:Myotonia / Q000201:enzymology; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism; D010805:Physical Conditioning, Animal
D006003:Glycogen; D008291:Malate Dehydrogenase; D006006:Glycogen Synthase; D010729:Phosphoenolpyruvate Carboxykinase (GTP)