Competition between extramitochondrial and intramitochondrial ATP-consuming processes.
The relationship between intra- and extramitochondrial ATP utilization was investigated in liver mitochondria isolated from normally fed, starved and high-protein fed rats. ATP export was provoked by adding a hexokinase-glucose-trap and intramitochondrial ATP consumption by adding ammonia, bicarbonate and ornithine in order to stimulate citrulline synthesis. Both processes compete for ATP produced via oxidative phosphorylation; the rate of citrulline formation declines as the extramitochondrial [ATP]/[ADP] ratio decreases. It is concluded that ATP for adenine nucleotide translocation and that for carbamoyl phosphate synthesis are delivered from a common intramitochondrial pool of adenine nucleotides. In mitochondria from rats with a high-protein diet, citrulline synthesis greatly stimulates the rate of oxidative phosphorylation (about two thirds of state 3 respiration). Under these conditions the intramitochondrial [ATP]/[ADP] ratio is significantly reduced. The intramitochondrial [ATP]/[ADP] ratio is not in thermodynamic equilibrium with the extramitochondrial one.
D000227:Adenine Nucleotides / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002222:Carbamoyl-Phosphate Synthase (Ammonia) / Q000378:metabolism; D002956:Citrulline / Q000096:biosynthesis*; D004044:Dietary Proteins; D006593:Hexokinase / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D051381:Rats; D013217:Starvation
D000227:Adenine Nucleotides; D004044:Dietary Proteins; D002956:Citrulline; D000255:Adenosine Triphosphate; D006593:Hexokinase; D000251:Adenosine Triphosphatases; D002222:Carbamoyl-Phosphate Synthase (Ammonia)