Citrulline synthesis--a tool for investigation of the mitochondrial energy metabolism.

The conditions under which citrulline synthesis can be used to stimulate mitochondrial energy metabolism were investigated in isolated rat liver mitochondria. At 25 degrees C, with glutamate as substrate, a lag phase of citrulline formation was observed, which was neither detectable in the presence of succinate nor at 38 degrees C with both substrates. After a high-protein diet, a stationary synthesis was seen from the beginning of incubation for both substrates at either temperature. The high-protein diet was applied to reach maximal citrulline synthesis. Citrulline production was found to be enhanced twice to three times as early as after one to two days. Citrulline formation and associated oxygen uptake vs. temperature were checked in the range from 10 degrees C to 42 degrees C. A linear relationship was noted between temperature and reaction rates in the Arrhenius plot, and the share of citrulline synthesis in the total energy transformation increased with rising temperature. Citrulline synthesis was adopted in experiments to determine the equilibrium state of the adenine nucleotide translocator at 38 degrees C. Just as at 25 degrees C, the translocator operated under disequilibrium conditions at body temperature, too, and the loss of free energy was--3.2 kJ X mol-1.