Abstract
The transport mechanism of the reconstituted ornithine/citrulline carrier purified from rat liver mitochondria was investigated kinetically. A complete set of half-saturation constants (Km) was established for ornithine, citrulline and H+ on both the external and internal side of the liposomal membrane. The internal affinity for ornithine was much lower than that determined on the external surface. The exclusive presence of a single transport affinity for ornithine on each side of the membrane indicated a unidirectional insertion of the ornithine/citrulline carrier into liposomes, probably right-side-out with respect to mitochondria. Two-reactant initial velocity studies of the homologous (ornithine/ornithine) and heterologous (ornithine/citrulline) exchange reactions resulted in a kinetic pattern which is characteristic of a simultaneous antiport mechanism. This type of mechanism implies that the carrier forms a ternary complex with the substrates before the transport reaction occurs. A quantitative analysis of substrate interaction revealed that rapid-equilibrium random conditions were fulfilled, characterized by a fast and independent binding of internal and external substrates.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Bioenergetics
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