Polydispersity and Heterogeneity of the Soluble Glycoprotein Isolated from Bovine Milk Fat Globule Membrane

Abstract

Polydispersity and heterogeneity of the soluble glycoprotein isolated from bovine milk fat globule membrane were demonstrated by means of isoelectric focusing and irnmunoelectrophoresis.
The soluble glycoprotein showed a polydispersity on isoelectrofocusing gels, and its isoelectric pH ranged from 4.4 to 5.7. SDS-polyacrylamide gel electrophoresis of the polydispersed glycoprotein fractions separated by the isoelectric focusing suggested that the polydispersity was caused by various stages of intermolecular association of the constituent polypeptides.
Immunoelectrophoretic experiments showed that there were at least four different antigenic compounds. The appearance of the major precipitin lines suggested the polydispersity of the glycoprotein.
These results indicate that the soluble glycoprotein from milk fat globule membrane is not homogeneous although an apparent homogeneity was observed in some ordinary physicochemical analyses.