SFXN4 is annotated in UniProt as a mitochondrial amino-acid transporter. Unlike some other members of its family, it does not act as a serine transporter: it is not able to mediate the transport of serine into mitochondria. The protein is a transmembrane component of the inner mitochondrial membrane, and it is required for mitochondrial respiratory homeostasis and for erythropoiesis, linking mitochondrial function to red blood cell development.

The SFXN4 gene encodes a member of the sideroflexin family, which UniProt and HGNC both recognise. HGNC places it in two gene groups: solute carrier family 56 (sideroflexins) and mitochondrial respiratory chain complex assembly factors. The latter classification reflects its role in respiratory chain function. Alternatively spliced transcript variants have been reported for the gene. The mouse ortholog is Sfxn4, which makes the murine gene a natural counterpart for functional studies of the human SFXN4 protein.

Mutations in the SFXN4 gene are associated with mitochondriopathy and macrocytic anaemia, which makes the protein of interest to researchers studying mitochondrial disease and disorders of erythropoiesis. The alias SLC56A4 follows the solute carrier nomenclature used for the sideroflexins. Related family members such as SFXN1 are often studied alongside SFXN4 when comparing the substrate specificity and physiological roles of mitochondrial amino-acid transporters.