The sideroflexin (SFXN) family is comprised of SFXN1, SFXN2, SFXN3, SFXN4 and SFXN5. SFXN1, also designated tricarboxylate carrier protein TCC, is the most highly characterized family member. The ubiquitously expressed SFXN1 protein resides as an integral protein of the mitochondrial inner membrane. It functions as an essential component of the shuttle system that transports mitochondrial acetyl-CoA into the cytosol, where lipogenesis occurs. The SFXN1 gene is mutated in flexed-tail (f/f) mice, which display axial skeletal abnormalities and a transient embryonic and neonatal anemia characterized by pathologic intramitochondiral iron deposits in erythrocytes. Therefore, SFXN1 is also thought to facilitate the transport of a component required for iron utilization into mitochondria. All SFXN family members show expression in pancreatic islet cells. SFXN5 displays a citrate transport activity and is primarily expressed in brain.