Characterization of epidermal growth factor binding to hepatic plasma membranes of rainbow trout ( Oncorhynchus mykiss)

Abstract

Epidermal growth factor (EGF) is a potent mitogen which exerts its effects through a transmembrane receptor located on target cells. Since little is known about EGF in non-mammalian animals, experiments were conducted to characterize the EGF receptor in rainbow trout hepatic cell membranes. The binding of mouse EGF with rainbow trout receptors was peptide-specific, saturable, reversible, and of high affinity. Optimal binding was observed at pH 7.2. Both monovalent and divalent cations augmented the specific binding of EGF, by a factor of two- to threefold over control values, but were not needed for binding to occur. Scatchard plot of the saturation data was curvilinear. Analysis of the data by kinetic methods indicated the curvilinear nature of the Scatchard plot was due to multiple receptor sites of differing affinity and not to site-to-site interactions. Rate constants for association ( K 11) were 9.38 × 10 8 M −1 ∗ min −1 and 2.28 × 10 7 M −1 ∗ min −1 for the high and low affinity sites, respectively. Rate constants for dissociation ( K −1) were 2.03 × 10 −3 min −1 and 2.07 × 10 −1 min −1 for high and low affinity sites, respectively. The apparent dissociation constants determined from the rate constants for the high affinity ( K D = 2.3 × 10 −11 M) and low affinity ( K D = 9.1 × 10 −9 M) were in agreement with constants estimated by equilibrium methods. Maximum binding capacities were 13 fmol EGF bound/mg protein of protein and 270 fmol EGF bound/mg of protein for the high and low affinity receptor sites, respectively. These experiments support the hypothesis that the EGF-receptor system has been evolutionarily conserved.