An intestinal receptor for heme.

Porcine upper small intestine took up radioactive heme in vitro. The binder was localised to the brush borders, was solubilized with Triton X-100 and bound heme with high affinity. The binding was inhibited with non-radioactive heme but not with FeSO4, and control experiments indicated that it was not any of the known heme binders or aggregated heme. The binding factor could also be solubilized from human duodenum.