It has been suggested that they accomplish this by secreting, upon need, a siderophore, a low-molecular-weight ligand displaying an elevated affinity for Fe3+ ions. The "Fe3+-siderophore" complex is subsequently moved in the cytoplasm, where it is cleaved. The ferric ions must then be converted into the ferrous form (Fe2+), to be accumulated within the BMP; this is achieved by means of a transmembrane transporter, which exhibits sequence homology with a Na+/H+ antiporter.