Background：

This multifunctional protein catalyzes the formation， breakage and rearrangement of disulfide bonds. At the cell surface， seems to act as a reductase that cleaves disulfide bonds of proteins attached to the cell. May therefore cause structural modifications of exofacial proteins. Inside the cell， seems to form/rearrange disulfide bonds of nascent proteins. At high concentrations， functions as a chaperone that inhibits aggregation of misfolded proteins. At low concentrations， facilitates aggregation (anti-chaperone activity). May be involved with other chaperones in the structural modification of the TG precursor in hormone biogenesis. Also acts a structural subunit of various enzymes such as prolyl 4-hydroxylase and microsomal triacylglycerol transfer protein MTTP.