An intestinal receptor for heme: Its partial characterization

Abstract 1. 1. An intestinal macromolecular heme ∗ binder both from human and porcine intestinal brush borders has been solubilized and partly purified. 2. 2. This heme binder is not albumin, hemopexin, glutathione- S -transferase or aggregated heme. Heme, but not intact hemoglobin seems to be bound to this binder. A 100-fold molar excess of FeSO 4 does not inhibit the uptake of heme by this binder. 3. 3. The dissociation constant of the binder-heme complex is 10 −6 to 10 −7 mol/l thus justifying the term heme receptor. 4. 4. Presumably a pathological or absent heme receptor could have an adverse effect on heme and iron absorption, especially as the absorption of heme iron is not affected by those blocking substances in food, which bind ionic iron.