A NOVEL GASTRIN-BINDING PROTEIN IN THE HUMAN EOSINOPHIL

A specific and saturable interaction between I-125-gastrin and eosinop hils was discovered in autoradiographs of human gastric mucosal tissue and confirmed in isolated and enriched preparations of WBC's. Gastrin displaced I-125-gastrin from eosinophils in a dose-dependent manner w ith a D-50 = 11 uM. Scatchard analysis of the saturation curve indicat ed a single binding site of low affinity (K-d = 4.14 uM) and high capa city (B-max = 430 umoles/mg protein). The gastrin binding protein was localized to the granular core of the eosinophil and found to have a m olecular weight of similar to 15 kDa following chemical crosslinking o f radioligand to granules and SDS/PAGE. Eased on its molecular weight and granular location and the charge characteristics of gastrin, the g astrin binding protein in the human eosinophil is most likely major ba sic protein. In vivo this interaction might act to limit the cytotoxic potential of MBP on tissues and/or attentuate gastrin concentrations thereby helping regulate gastric acid secretion and mucosal growth. (C ) 1998 Academic Press.