Characterization of the receptor for epidermal growth factor-urogastrone in human placenta membranes.
The binding of mouse epidermal growth factor-urogastrone (EGF-URO) to membranes from term human placenta is peptide-specific, saturable (about 20 pmol of EGF-URO bound maximally/mg of protein), reversible, and of high affinity (KD about 400 pM). Optimal binding is observed at pH 7.6. At low pH (3.5 to 5.0). EGF-URO can be reversibly dissociated from the receptor; however, exposure to pH < 3 irreversibly inactivates the receptor. The binding, which does not exhibit ligand cooperativity, exhibits an association rate constant of 6.1 x 10(-4) s-1 and a dissociation rate constant of 6.1 x 10(-4) s-1. The dissociation constant determined from the rate constants, 240 pM, is in reasonable agreement with the constant estimated by equilibrium methods. Both monovalent and divalent cations augment EGF-URO binding 2- to 3-fold. Although in general, divalent cations enhance binding at lower concentrations (optimum, 5 mM) than do monovalent cations (optimum, approximately 80 mM), there is no cation-specific effect. Neither guanine nor adenine nucleotides affect EGF-URO binding. Whereas the proteolytic enzymes (trypsin, chymotrypsin, papain, and pepsin) inactivate the receptor, neuraminidase and phospholipases A2, C, and D augment EGF-URO binding. Neuraminidase increases the number of available sites without affecting ligand affinity. Wheat germ agglutinin, concanavalin A, and phytohemagglutinin all compete for the binding of EGF-URO. The data complement previous observations of EGF-URO binding obtained in intact cells and provide a basis for the solubilization, characterization, and isolation of this receptor from a rich tissue source.
D000818:Animals; D002413:Cations, Divalent; D002414:Cations, Monovalent; D002462:Cell Membrane / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors; D005260:Female; D005768:Gastrointestinal Hormones / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D037102:Lectins / Q000494:pharmacology; D051379:Mice; D010455:Peptides / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000378:metabolism*
D002413:Cations, Divalent; D002414:Cations, Monovalent; D005768:Gastrointestinal Hormones; D037102:Lectins; D010455:Peptides; D011956:Receptors, Cell Surface; D004815:Epidermal Growth Factor; D066246:ErbB Receptors