A single purification procedure for the major resident proteins of the ER lumen: endoplasmin, BiP, calreticulin and protein disulfide isomerase.

We have developed a single purification procedure for the four major resident endoplasmic reticulum (ER) proteins: protein disulfide isomerase (PDI), BiP, endoplasmin, and calreticulin. Three of these proteins are thought to play a role in protein folding in vivo, whereas calreticulin is thought to be the major calcium binding protein in the ER. The proteins were purified from fresh bovine liver by taking advantage of individual characteristics of the proteins. Liver microsomes were prepared and then premeabilized to release the lumenal contents. After ammonium sulfate precipitation, the proteins were purified by chromatography; BiP was purified by affinity chromatography on ATP-agarose, and both endoplasmin and calreticulin were purified by affinity chromatography on Con A-Sepharose. PDI was purified by anionic ion exchange chromatography.