pH Sensitivity of epidermal growth factor receptor complexes

The association/dissociation binding kinetics of ¹²⁵I‐labeled mouse epidermal growth factor (EGF) to receptors on human fibroblast cells in monolayer culture have been measured at 4°C as a function of extracellular pH from pH 5–9. At pH 8, steady‐state total binding is maximal. As pH is lowered to 6.5, total binding monotonically decreases dramatically. It changes further only slightly between pH 6.5 and 5 to about 20% of the maximum binding value. Scatchard binding plots at pH 7.5 and above show the commonly observed concave‐upward, non‐linear curve; as pH is lowered, this plot becomes much more linear, indicating that the “high affinity” bound receptor population is greatly diminished. Application of our ternary complex binding model [Mayo et al., J Biol Chem 264:17838–17844, 1989], which hypothesizes complexation of the EGF‐bound receptor with a cell surface interaction molecule, indicates that pH may have some direct effects on ternary complex formation, but the major effect is on EGF‐receptor dissociation. © 1993 Wiley‐Liss, Inc.