Human and Bovine Milk Contain Different Sets of Growth Factors*

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Abstract
Growth factor activity is present in human milk throughout the lactation period but is in bovine milk only during the colostral phase. Biochemical analysis shows that the growth factors in human and bovine milk are not the same. Human milk contains 3 spp. of growth factors. One of these, designated human milk growth factor (HMGF) III, constitutes > 75% of the total growth factor activity of human milk. HMGF III has a MW of .apprx. 6000, a pI between 4.4 and 4.7, and is resistant to treatment with dithiothreitol. Comparative biochemical studies strongly suggest that HMGF III is a human epidermal growth factor (EGF). On the other hand, bovine colostrum has no EGF-like growth factor. Instead, the major growth factor component of bovine colostrum has a MW between 30,000 and 35,000 and is inactivated by dithiothreitol treatment. The bovine colostrum growth factor (BCGF) is similar biochemically to one of the minor growth factors in human milk, HMGF II, which accounts for .apprx. 20% of the growth factor activity of human milk. HMGF III, the EGF-like polypeptide, can be purified to homogeneity by a combination of size exclusion and anion exchange chromatography. Purified HMGF III stimulates DNA synthesis in mouse fibroblast 3T3 cells at a concentration of .apprx. 25 ng/ml.