Spectral and other studies on the intestinal haem receptor of the pig

We recently demonstrated the presence of a Triton-solubilized high-affinity haem binder on the pig duodenal brush border membrane. The association of haem to the binding factor was determined using radioactive haem and is now studied by a spectrophotometric technique. The binding alters the Soret absorption band of haem from 395 nm to 413 nm. The dissociation constant for the binding of haem to the solubilized binding factor was estimated to be about 10(-9) M by difference spectroscopy. Human serum albumin could not prevent the solubilized binding factor from binding haem. Trypsin digestion destroyed the binder.