Transmembrane reductase that uses ascorbate as an electron donor in the cytoplasm and transfers electrons across membranes to reduce iron cations Fe(3+) into Fe(2+) in the lumen of the late endosome and lysosome. Reduced iron can then be extruded from the late endosome and lysosome to the cytoplasm by divalent metal-specific transporters. It is therefore most probably involved in endosomal and lysosomal cellular iron homeostasis. Fe(3+)(out) + L-ascorbate(in) = Fe(2+)(out) + H(+) + monodehydro-L-ascorbate radical(in) Binds 2 heme b groups non-covalently. Homodimer. Extended N-terminus.