title: Association and dissociation of Escherichia coli heat-stable enterotoxin from rat brush border membrane receptors.
abstract: Escherichia coli heat-stable enterotoxin (ST) binds to receptors on rat intestinal cells and brush border membranes (BBM). We devised experiments to examine the reversibility of ST binding. We found that both 125I-labeled ST and native ST were spontaneously dissociable from the BBM receptor. Radiolabeled ST bound to BBM was also dissociated by the addition of avid goat anti-ST antiserum. Furthermore, using a computer program for analysis of ligand binding, we calculated an apparent Ka of 10(8) liters/mol from competitive inhibition and saturation-binding data. This is significantly lower than the value previously reported by others. Our findings, of a lower Ka and a reversible ST-binding process, suggest that a therapeutic strategy of removing bound ST from its receptor or competing with the enterocyte receptor for unbound ST might be successful in terminating ST-induced secretion.
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D004768:Enterotoxins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D006162:Guanylate Cyclase; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008297:Male; D008871:Microvilli / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D011971:Receptors, Immunologic / Q000378:metabolism*; D018000:Receptors, Peptide
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D007457:Iodine Radioisotopes; D011971:Receptors, Immunologic; D018000:Receptors, Peptide; C034151:heat stable toxin (E coli); D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled