ABSTRACT
This chapter concerns primarily with possible mechanisms of transmembrane signaling by the receptor in response to the binding of epidermal growth factor (EGF). The precursor also contains seven to nine EGF-related sequences of unknown function, and a putative transmembrane segment near the carboxyl terminus. The physiological roles of EGF and related growth factors in vivo are as yet unclear, though some in vivo activities of EGF have been noted. The observation of specific saturable binding of I-EGF to human fibroblasts first suggested the existence of specific cell surface receptors for EGF. They were not, however, sufficient to distinguish between a strong noncovalent association and a covalent connection between the receptor and the kinase. H. Ushiro and S. Cohen demonstrated that the EGF-stimulated PK is specific for tyrosyl residues, making it the first PK involved in normal cellular metabolism found to have such specificity.
