In 1962, Cohen reported the isolation of a polypeptide from the submaxillary gland of male mice that accelerated eyelid opening and incisor eruption in the newborn animal. This polypeptide, epidermal growth factor (EGF), was subsequently found to stimulate proliferation and keratinization of mouse epidermis in vivo and the growth of chick embryo epidermis in vitro.
EGF is a low-molecular-weight polypeptide. The molecular weight (MW) of EGF is approximately 6,400 daltons. However, in crude homogenates of the submaxillary gland of the male mouse, EGF exists almost entirely in a high molecular weight complex (about 74,000 daltons). This high molecular weight form may be reversibly dissociated into EGF and a protein of molecular weight 29,000. This EGF-binding protein is an esterase with an apparent high degree of specificity for arginine esters
EGF is characterized by the absence of three specific amino acids: lysine, phenylalanine, and alanine. Low molecular weight EGF as isolated from high-molecular-weight EGF showed an identical amino acid analysis, further documenting its identity with Cohen's original EGF.