Occurrence of High Molecular Weight EGF Complexes in Human Milk

Abstract

A survey was conducted of the cell-growth-promoting factors in human milk using anti-human EGF antiserum and by a DNA synthesis assay in BALB/c mouse 3T3 embryo fibrpblast cells. Three fractions having affinity toward anti-human EGF antibody were found by gel filtration on Sephacryl S-300. The fraction eluted at the void volume and the one with a molecular weight of about 70, 000 both showed weak DNA synthesis stimulatory activity. On the other hand, the one with a molecular weight of about 6, 000 highly stimulated DNA synthesis. This fraction was thought to contain EGF, whose molecular weight is about 6, 000. Rechromatography by gel permeation again separated both the two high molecular weight peaks into 3 peaks and produced similar chromatograms. The results suggest that these 3 fractions may have been in an apparent equilibrium state. Considering that the EGF-fraction of molecular weight 6, 000 did not show self-association, it is presumed that an EGF binding protein exists in human milk and forms higher molecular weight EGF complexes.