G-1,6-P2 in human skeletal muscle after isometric contraction.
The content of glucose 1,6-bisphosphate (G-1,6-P2), an in vitro activator of phosphofructokinase (a rate-limiting enzyme for glycolysis), and the glycolytic rate in skeletal muscle during isometric contraction have been determined. Subjects contracted the knee extensor muscles at two-thirds maximal voluntary force to fatigue. Biopsies from the quadriceps femoris muscle were obtained before and immediately after contraction. G-1,6-P2 increased in all subjects from a mean of 101 +/- 15 (SE) mumol/kg dry wt at rest to 128 +/- 24 at fatigue (P less than 0.05). Muscle glucose did not change significantly, whereas hexosemonophosphates were significantly increased after contraction. The glycogenolytic and glycolytic rate averaged 70.0 +/- 13.8 and 47.3 +/- 6.7 mmol.kg dry wt-1.min-1, respectively, and the glycolytic rate was positively correlated with the accumulation rates of fructose 6-phosphate (F-6-P) (r = 0.95, P less than 0.01) and G-6-P (r = 0.96, P less than 0.01). Phosphocreatine and ATP decreased by 87 and 17%, respectively, whereas ADP increased by 31% after contraction. These data demonstrate that intense, short-term isometric contraction results in an elevation of the muscle content of G-1,6-P2. The increase in G-1,6-P2 could not be accounted for by the side reactions of phosphoglucomutase or phosphofructokinase. It remains to be determined whether the observed increase in G-1,6-P2 is sufficient to account for the high glycolytic rate during intense exercise. The lack of increase in muscle glucose while G-6-P increased (which will inhibit hexokinase) suggests that the debranching enzyme complex was not active during contraction.
Katz
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Clinical Diabetes and Nutrition Section, National Institutes of Diabetes and Digestive and Kidney Disease, Phoenix 85016.
Lee
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AD
D000227:Adenine Nucleotides / Q000378:metabolism; D000328:Adult; D003401:Creatine / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives*; D005958:Glucosephosphates / Q000378:metabolism*; D006600:Hexosephosphates / Q000378:metabolism; D006801:Humans; D007537:Isometric Contraction; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism
D000227:Adenine Nucleotides; D005958:Glucosephosphates; D006600:Hexosephosphates; D010725:Phosphocreatine; D019298:Glucose-6-Phosphate; C016473:glucose-1,6-bisphosphate; D003401:Creatine