This gene encodes a member of the disulfide isomerase (PDI) family of endoplasmic reticulum (ER) proteins that catalyze protein folding and thiol-disulfide interchange reactions. The encoded protein has an N-terminal ER-signal sequence, a catalytically active thioredoxin domain, and one transmembrane domain. Unlike most members of this gene family, it lacks a C-terminal ER-retention sequence. The mature membrane-bound protein can both oxidize and reduce disulfide bonds and acts selectively on membrane-associated polypeptides.