Proteins mask gangliosides in milk fat globule and erythrocyte membranes

Ganglioside in the membrane of erythrocytes and the fat globules of cow's milk were not degraded by neuraminidase treatment at pH 5.2 or 7.4. Removal of portions of the membrane protein by treatment with trypsin or by extraction with a solution of EDTA and 2-mercaptoethanol rendered these membrane-associated gangliosides accessible to neuraminidase attack. After trypsin treatment under conditions where the membranes are impermeant to this enzyme, gangliosides were exposed to neuraminidase. The results suggest that the carbohydrate groups of the gangliosides of bovine erythrocytes and milk fat globules are located primarily on the environmental face of the membrane and are shielded from neuraminidase attack by membrane proteins.