<p>This entry represents protein disulphide-isomerase A4 (also known as endoplasmic reticulum protein 72 kDa or ERp-72) (<db_xref db="EC" dbkey="5.3.4.1"/>), which acts as a molecular ER chaperone. ER chaperones are critical not only for quality control of proteins processed in the ER, but also for regulation of ER signalling in response to ER stress [<cite idref="PUB00044648"/>]. ERp-72 catalyses the rearrangement of -S-S- bonds in proteins. It is part a large chaperone multiprotein complex comprising CABP1, DNAJB11, HSP90B1, HSPA5, HYOU, PDIA2, PDIA4, PPIB, SDF2L1, UGT1A1 and very small amounts of ERP29, but not, or at very low levels, CALR nor CANX. ERp-72 may functionally associate with NADPH oxidase 1 (NOX1) [<cite idref="PUB00044649"/>].</p>