Isolation, Purification and Characterization of Fatty-Acid-Binding Protein from Milk Fat Globule Membrane: Effect of Bovine Growth Hormone Treatment

Fatty-acid-binding protein (FABP) was purified from bovine milk fat globule membrane (MFGM) by ion-exchange chromatography on DEAE-Sepharose and by gel-filtration on Sephadex G-50. Purified FABP was similar to bovine mammary gland heart (H)-type FABP/ mammary derived growth inhibitor (MDGI). It inhibited growth of mammary epithelial cells at nanogram concentrations, had a relative molecular mass of 15 kDa, as determined by SDS-PAGE, had two isoforms with pI around 5.0 and cross-reacted with antibody to mammary gland H-FABP. The content of FABP in MFGM, obtained from growth hormone (GH)-treated cows, was not essentially different from that of MFGM obtained from untreated cows. However, the level of in vitro phosphorylated FABP of MFGM, obtained from GH-treated cows, was diminished in comparison to the sample of MFGM, obtained from untreated cows. The role of the insulin receptor in the phosphorylation of FABP in mammary gland secretory epithelial cells is suggested.