UPTAKE OF EXOGENOUS GANGLIOSIDES BY RAT-BRAIN SYNAPTOSOMES

Synaptosomes incorporated mixed brain gangliosides at a rapid initial rate followed by a slower phase of net movement from the protein-assoc iated fraction into the membrane core. The pattern of incorporated gan gliosides reflected the pattern available for incorporation. Intact sy naptosomes incorporated similar to 100 pmol GM1/mg protein. Synaptosom es preincubated with proteolytic enzymes (trypsin, chymotrypsin, and p apain) at different pH values (6.2, 7.4, 7.8) incorporated more exogen ous gangliosides than synaptosomes preincubated in buffer alone. This effect was maximal at pH 7.8, though analysis of variance revealed tha t the proteolytic treatment and pH effects were probably independent p rocesses. Overall uptake of exogenous gangliosides correlated signific antly with amount of membrane protein loss, indicating that initial ac cess of exogenous gangliosides to synaptosomal membranes is retarded b y cell-surface proteins. These results suggest synaptosomes as a usefu l alternative to cultured cells for investigating the interaction of g angliosides with other cell surface constituents.