Oxidoreductase involved in disulfide bond formation in the endoplasmic reticulum. Efficiently reoxidizes pdi-1, the enzyme catalyzing protein disulfide formation, in order to allow pdi-1 to sustain additional rounds of disulfide formation. Following pdi reoxidation, passes its electrons to molecular oxygen via FAD, leading to the production of reactive oxygen species (ROS) in the cell (By similarity). May function both as a monomer and a homodimer. Belongs to the EROs family.