Control of glycogenosis in rainbow trout muscle during exercise

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Abstract
The purpose of this study was to measure and compare the in vivo levels of glycolytic pathway intermediates during high-intensity, progressive exercise in rainbow trout red and white muscle. The mass action ratios of those reactions catalyzed by the enzymes hexokinase, phosphofructokinase, and pyruvate kinase appear to be displaced far from thermodynamic equilibrium (greater than log 2) under all experimental conditions in both tissue types. Furthermore, the near-equilibrium glyceral-dehyde 3-phosphate dehydrogenase – phosphoglycerate kinase complex deviated from thermodynamic equilibrium during the exhaustive swim for white muscle and for all exercise intensities in red muscle. The mass action ratio of the combined glyceraldehyde 3-phosphate dehydrogenase – phosphoglycerate kinase/lactate dehydrogenase demonstrated displacements from thermodynamic equilibrium similar to those of the glyceraldehyde 3-phosphate dehydrogenase complex. Potential control sites were identified as phosphorylase for white muscle and hexokinase and glyceraldehyde 3-phosphate dehydrogenase – phosphoglycerate kinase for red muscle. No alterations in potential control sites were found in white muscle with changing flux rates (sustained and burst swims) provided sufficient glycogen was available as precursor. Phosphofructokinase and glyceraldehyde 3-phosphate dehydrogenase only demonstrated potential control in this tissue when glycogen content and flux rates were low (exhaustive swim). These changes coincided with substrate depletion to low levels and large declines in the ATP/ADPf ratio. Therefore, it would appear that glycogen content is the primary factor regulating glycolytic flux and control sites via alterations in adenylate levels.