Transmembrane reductase that may use ascorbate as an electron donor in the cytoplasm and transfer electrons across endoplasmic reticulum membranes to reduce monodehydro-L-ascorbate radical and iron cations Fe(3+) in the lumen of that compartment. L-ascorbate(in) + monodehydro-L-ascorbate radical(out) = L-ascorbate(out) + monodehydro-L-ascorbate radical(in) Fe(3+)(out) + L-ascorbate(in) = Fe(2+)(out) + H(+) + monodehydro-L-ascorbate radical(in) Binds 2 heme b groups non-covalently. Optimum pH is 6-7 for the electron donation reaction to monodehydroascorbate reaction (PubMed:23641721). Optimum pH is around 6.5 for re-reduction reaction process of the oxidized heme with ascorbate (PubMed:23641721). E(0) is +89.5 mV for the high potential heme and +13.1 mV for the low potential heme (PubMed:19734123). E(0) is +109 mV for the high potential heme and +26 mV for the low potential heme (PubMed:23235316).