Study on the susceptibility of the bovine milk fat globule membrane proteins to enzymatic hydrolysis and organization of some of the proteins

Isolated milk fat globules were subjected to enzyme hydrolysis by a specific protease (trypsin) and a non-specific protease (pronase E) to study the asymmetric arrangement of milk fat globule membrane (MFGM) proteins. The remaining proteins on the globules after proteolysis were resolved by two-dimensional gel electrophoresis and identified by mass spectrometry. By this proteomic approach, the results confirmed different susceptibility of the MFGM proteins to proteolysis by enzymes. Butyrophilin and adipophilin were completely digested by trypsin and by pronase E, whereas lactadherin and xanthine dehydrogenase/oxidase were almost resistant to hydrolysis by trypsin and partially attacked by pronase E. Based on our results and recent bibliographic data, an up-dated model of the organization of some MFGM proteins is proposed and discussed.