Protein disulfide isomerase of the endoplasmic reticulum lumen involved in the formation of disulfide bonds in proteins (PubMed:12930873, PubMed:14971039). Can reduce insulin disulfide bonds (PubMed:14971039). Catalyzes the rearrangement of -S-S- bonds in proteins. Expressed at high levels in plasma cells and at very low levels in all other cells and tissues examined (at protein level). Belongs to the protein disulfide isomerase family.