Solubilization and preliminary characterization of the human ileal vitamin B12-intrinsic factor receptor

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Abstract
The human ileal intrinsic factor receptor was solubilized with Triton X-100 using an improved method originally devised for the porcine receptor. At pH 7.4 and in the presence of Ca2 + the receptor bound the vitamin B12 complexes of normal human and pig intrinsic factor but not that of an abnormal biologically inert human intrinsic factor. EGTA dissociated vitamin B12-intrinsic factor from the receptor complexes. The solubilized vitamin B12-intrinsic factor receptor complex consisted of three to four molecular species termed HC-L, HC-20 S, HC-12 S and HC-8.5 S (the three last-mentioned referring to sedimentation coefficients). Of these HC-20 S was the dominating component and had a Stokes radius of 18 nm. Radioactive calcium was shown to be bound to vitamin B12-intrinsic factor and to be contained in its complex with the receptor.