Mitochondrial citric acid cycle and related enzymes: Adaptive response to exercise

The levels of activity of citrate synthase and of DPN-specific isocitrate dehydrogenase increased 2-fold in muscles of rats subjected to a program of running. A parallel increase occurred in the concentration of cytochrome c and in the level of activity of succinate dehydrogenase. In contrast, glutamate dehydrogenase activity increased approximately 35%, while the levels of α-ketoglutarate dehydrogenase and mitochondrial malate dehydrogenase increased 50%. These findings provide evidence that, unlike the constituents of the respiratory chain, the mitochondrial citric acid cycle and citric acid cycle related enzymes do not increase in parallel during the adaptive response of skeletal muscle to exercise, resulting in a change in mitochondrial composition.