protein-containing complex ferritin complex ferritin complex A protein complex that binds iron and acts as a major iron storage system. There are three major subclasses of ferritins: the classical ferritins (Ftn), the heme-containing bacterioferritins (Bfr) and the DNA-binding proteins from starved cells (Dps). Ftn and Bfr are made of 24 subunits, whereas Dps are smaller with 12 subunits. Ftn is found in most kindoms, while Bfr and Dps are restricted to prokaryotes.