Putative ferric-chelate reductases reduce Fe(3+) to Fe(2+) before its transport from the endosome to the cytoplasm. Binds 2 heme b groups non-covalently. Belongs to the FRRS1 family. The cytochrome b561 domain lacks the conserved His residue that binds iron in the heme. The reductase activity is therefore unsure in vivo.