Analysis of the control of citrulline synthesis in isolated rat-liver mitochondria.

The amount of control of the various steps involved in the citrulline synthesizing pathway in isolated rat-liver mitochondria incubated with saturating concentrations of ammonia and ornithine has been measured. The flux control coefficient of carbamoyl-phosphate synthase (ammonia) was close to one. Control exerted by other steps in the pathway, including ornithine transcarbamoylase, carbonic anhydrase. ATP production and transport of ornithine, was negligible. The high flux control coefficient of carbamoyl-phosphate synthetase is due to the low elasticity coefficient of this enzyme towards its product, intramitochondrial carbamoyl phosphate, in combination with a high elasticity coefficient of ornithine transcarbamoylase towards carbamoyl phosphate.