Cytochrome b561 (Cyb561) is an electron transfer protein unique to neuroendocrine secretory vesicles in animals [, ]. It has ferric reductase activity []. Bovine Cyb561 is a 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 [, , ].
Cytochrome b561 is a ferric-chelate reductase that reduces Fe3+ to Fe2+ before its transport from the endosome to the cytoplasm. It probably uses ascorbate as an electron donor [, ].
