Enables transmembrane monodehydroascorbate reductase activity. Involved in ascorbate homeostasis and cellular iron ion homeostasis. Located in chromaffin granule membrane. Is expressed in several structures, including alimentary system; genitourinary system; nervous system; node; and nose. Orthologous to human CYB561 (cytochrome b561). [provided by Alliance of Genome Resources, Apr 2022]