Relationship between the rate of citrulline synthesis and bulk changes in the intramitochondrial ATP/ADP ratio in rat-liver mitochondria.

1. The relationship between intramitochondrial and extramitochondrial ATP-utilizing systems and the intramitochondrial ATP/ADP ratio was studied in isolated rat-liver mitochondria. Citrulline synthesis was used as an intramitochondrial ATP-utilizing system, and glucose-6-phosphate synthesis as an extramitochondrial ATP-utilizing system. The intramitochondrial ATP/ADP ratio was manipulated in three ways: with succinate and different concentrations of malonate and/or hexokinase; with 2-oxoglutarate (plus oligomycin) and different concentrations of hexokinase; and with added ATP in uncoupled mitochondria (oligomycin present). 2. Under all conditions used, citrulline synthesis was strictly correlated with the bulk intramitochondrial ATP/ADP ratio. 3. The curve relating citrulline synthesis and intramitochondrial ATP/ADP was shifted towards lower ATP/ADP ratios when the activity of carbamoyl-phosphate synthetase was enhanced by increasing the mitochondrial content of N-acetylglutamate. 4. It is concluded that under the experimental conditions used the intramitochondrial adenine nucleotides behave as a homogeneous pool.