Mitochondrial amino acid transporters can be subdivided on the basis of their substrates. Mitochondrial ornithine transporters play a role in the urea cycle by exchanging cytosolic ornithine (L-ornithine and D-ornithine) for mitochondrial citrulline (L-citrulline and D-citrulline) in equimolar amounts. Further members of the family include transporters of S-adenosylmethionine and carnitine.

Both ornithine transporters are inhibited by the polyamine spermine [2]. Loss-of-function mutations in these genes are associated with hyperornithinemia-hyperammonemia-homocitrullinuria.

* Key recommended reading is highlighted with an asterisk

* Hewton KG, Johal AS, Parker SJ. (2021) Transporters at the Interface between Cytosolic and Mitochondrial Amino Acid Metabolism. Metabolites, 11 (2). [PMID:33669382]

1. Fiermonte G, Dolce V, David L, Santorelli FM, Dionisi-Vici C, Palmieri F, Walker JE. (2003) The mitochondrial ornithine transporter. Bacterial expression, reconstitution, functional characterization, and tissue distribution of two human isoforms. J Biol Chem, 278 (35): 32778-83. [PMID:12807890]

2. Fiermonte G, Paradies E, Todisco S, Marobbio CM, Palmieri F. (2009) A novel member of solute carrier family 25 (SLC25A42) is a transporter of coenzyme A and adenosine 3',5'-diphosphate in human mitochondria. J Biol Chem, 284 (27): 18152-9. [PMID:19429682]