SLC25A26 (S-adenosylmethionine mitochondrial carrier protein) associated with the inner mitochondrial membrane mediates the exchange of cytosolic AdoMet (S-adenosylmethionine) for mitochondrial AdoHcy (S-adenosylhomocysteine). The substrate specificity and countertransport function of SLC25A26 were established from studies of liposomes reconstituted with purified protein in vitro (Agrimi et al. 2004). SLC25A26 mutations that disrupt transport activity have been identified in patients with defects of mitochondrial function, consistent with a requirement for AdoMet uptake from the cytosol to support mitochondrial methylation reactions (Kishita et al. 2015).