| Abstrakt: |
The glycoproteins, Components 15/16 and GP 55, were partially purified from bovine and guinea-pig fat-globule membrane (FGM), respectively. Peptides prepared from immunoblots of Component 16 and GP 55, were shown by sequencing, to be similar to mouse MFG-E8 and a human milk protein of M(r) 46,000. Both of these latter proteins are associated with the FGM and contain epidermal growth factor-like domains and/or factor V/VIII-like sequences. These data complement earlier biochemical studies on the biosynthesis, tissue distribution and topology of Components 15/16 and GP 55, and indicate that MFG-E8-like proteins are expressed on the apical surfaces of mammary epithelial cells and are secreted both in a soluble form and as major components of the FGM in diverse species. The possible function of these proteins in lactation and in mammary and neonatal development is discussed. |
