The effect of hypoxia on carbohydrate metabolism in flounder ( Platichthys flesus L.)—II. High energy phosphate compounds and the role of glycolytic and gluconeogenetic enzymes

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1. 1. ATP, ADP, AMP, energy charge potential and total adenylates in heart, kidney and muscle are relatively unaffected by environmental hypoxia. In the liver, hypoxia causes a 90% drop in ATP, a rise in ADP and AMP, and a drop in energy charge potential and total adenylates. In the muscle tissue ATP concentration is stabilized by a large creatine phosphate pool. 2. 2. Hexokinase activity in the heart is 20 times higher than in the swimming muscle, and thus the heart has a high potential for utilizing exogenous glucose as an anaerobic substrate. 3. 3. The role of creatine phosphate in regulating muscle glycolysis is discussed on background of the strong inhibition of muscle phosphofructokinase by physiological concentrations of creatine phosphate. 4. 4. Flounder heart has a dominating M-type lactate dehydrogenase which is identical to the muscle enzyme by electrophoretic and kinetic criteria. This improves the anaerobic capabilities of the flounder heart compared to other fish hearts. 5. 5. Both liver and kidney have high activities of the gluconeogenetic enzymes glucose-6-phosphatase, fructose-1,6-diphosphatase, and phosphoenolpyruvate carboxykinase and both are capable of synthesizing glucose from [ 14C]lactate. Because of more favorable energy conditions in the kidney this organ may substitute the liver as a gluconeogenetic organ during hypoxia.