Abstract
Epidermal growth factor (EGF) is a polypeptide that has been isolated from mouse salivary gland and human urine. EGF stimulates proliferation of epidermal tissues of new born animals and causes precocious eye lid opening. In addition, like other so called growth factors, it is a potent mitogen for fibroblasts from various speicies. Recently, urogastrone, a potent inhibitor of gastirc acid secretion, was isolated from human urine. It bore a marked structual relationship to the EGF and now urogastrone is considered to be the same as human EGF.
Although extensive studies have been carried out with EGF, its physiological role remain uncertain. It binds to the specific plasma membrane receptors, and this is the first step in its biologic action as other peptide hormones. Therefore, tissue distribution of specific binding site for mouse EGF was studied. Tissue homogenate in 50 mM Tris-HCl buffer pH 7.4 were centifuged at at 12,000 xg. The resultant pellet was resuspended in the above buffer containing 0.1% BAS and 10mM MgCl2 and incubated with 0.5 ng of 125I-mouse EGF for 90 min at 20°. The incubation was terminated by adding ice cold buffer, and tissue bound 125I-EGF was separated by centrifugation. Specific binding sites for EGF were demonstrated in a variety of tissue, being the greatest per unit of protein in mouse liver. Scatchard analysis revealed that EGF receptor from mouse liver had apparent Kd 1.5×10-10 M with binding capacity of 25 f moles/mg tissue protein.
A specific radioreceptor assay was developed using the mouse liver capable of detecting 100pg of EGF. RRA values for EGF content in mouse submaxillary gland were in agreement with those obtained by radioimmunoassay. EGF like activity were detected by RRA in the submaillary gland and in urine of various species including human. Physicochemical characterization of EGF like substance in human urine showed it was identical with urogastrone. Thus this simple, rapid RRA for EGF is available for detecting and purifmg EGF of various species.
