Transmembrane reductase that uses ascorbate as an electron donor in the cytoplasm and transfers electrons across membranes to reduce monodehydro-L-ascorbate radical in the lumen of secretory vesicles. It is therefore involved the regeneration and homeostasis within secretory vesicles of ascorbate which in turn provides reducing equivalents needed to support the activity of intravesicular enzymes. L-ascorbate(in) + monodehydro-L-ascorbate radical(out) = L-ascorbate(out) + monodehydro-L-ascorbate radical(in) Binds 2 heme b groups non-covalently. Secretory vesicle containing catecholamines and amidated peptides.