Isolation of rat epidermal growth factor (r-EGF): chemical, biological and immunological comparisons with mouse and human EGF.

Rat epidermal growth factor, (r-EGF), was isolated from adult male rat submandibular glands, with final yields of 4-6 mg r-EGF from 20 to 25 g wet weight of tissue. Amino acid analysis of r-EGF indicated a high degree of homology with murine EGF (m-EGF) and human EGF, (h-EGF). However, r-EGF contains 49 amino acid residues, versus 53 for human and murine EGFs, and lacks two characteristic tryptophan residues present in the other two species. The lack of tryptophan residues did not affect cellular binding or mitogenic activity or r-EGF. Polyclonal antisera to each of the three separate species demonstrated crossreactivity with the other species of EGF. A sensitive radioimmunoassay was developed for r-EGF which can detect 25 pg of hormone.