Characteristic and Localization of the Monitor Peptide Receptor

The monitor peptide receptor in the small intestine was investigated. The receptor is on the intestinal mucosal cells [Biochem. J., in press]. The specific binding of the (125)I labeled monitor peptide to dispersed rat small intestinal cells was inhibited by treatment with p-toluensulfonyl-L-lysine chloromethyl ketone (TLCK), an affinity labeling reagent for trypsin. Soybean trypsin inhibitor (SBTI) did not inhibit the binding. Analysis with reduced SDS electrophoresis-autoradiography indicated that an affinity-cross-linked complex of the (125)I labeled monitor peptide and the receptor was abolished by the TLCK treatment but was not affected by the presence of SBTI. Histochemical studies found a predominatnt binding of (125)I labeled monitor peptide on cholecystokinin (CCK)-immunoreactive cells in tissue sections of the rat upper intestine. The result suggests that the monitor peptide receptor is on the surface of CCK-producing cells.