Purification of the intestinal receptor for intrinsic factor by affinity chromatography

The intestinal receptor for the intrinsic factor vitamin B-12 complex has been solubilized and then purified from the guinea pig ileum using a double structured affinity resin comprised of intrinsic factor coupled to vitamin B-12 which, in turn, was covalently linked to Sepharose 4B. The receptor purified approximately 57 000-fold from the crude homogenate, appears to be a homogenous protein which may be composed of two subunits which separated when the preparation was subjected to polyacrylamide disc gel electrophoresis. Ethylenediaminetetraacetic acid induced dissociation of the complex between the purified receptor and intrinsic factor-B-12 could not be reversed by the addition of excess Ca2+, unlike the effect of EDTA with semipurified receptor or crude ileal homogenates. Calcium reversed the EDTA effect only after the mixture was subjected to extensive dialysis suggesting that the chelating agent interacts directly with the receptor protein. Intrinsic factor-vitamin B-12 competively inhibited the binding of intrinsic factor-[57Co] vitamin B-12 to the purified receptor whereas vitamin B-12 free intrinsic factor did not, even at a 100-fold greater concentration.