Acts as a membrane-bound chaperone in endoplasmic reticulum quality control. Probably facilitates presentation of substrate to membrane-bound components of the degradation machinery. Catalyzes the rearrangement of -S-S- bonds in proteins. Interacts with mutated PMA1-D378N but not wild type PMA1. Interacts with EUG1, KAR2, MPD1 AND PDI1. Present with 6020 molecules/cell in log phase SD medium. Belongs to the protein disulfide isomerase family.