Plasma membrane reductase that uses cytoplasmic ascorbate as an electron donor to reduce extracellular Fe(3+) into Fe(2+). It is also able to reduce extracellular monodehydro-L-ascorbate and may be involved in extracellular ascorbate regeneration (By similarity). May also function as a cupric transmembrane reductase (By similarity). Fe(3+)(out) + L-ascorbate(in) = Fe(2+)(out) + H(+) + monodehydro-L-ascorbate radical(in) Cu(2+)(out) + L-ascorbate(in) = Cu(+)(out) + H(+) + monodehydro-L-ascorbate radical(in) L-ascorbate(in) + monodehydro-L-ascorbate radical(out) = L-ascorbate(out) + monodehydro-L-ascorbate radical(in) Binds 2 heme b groups non-covalently. Homodimer.