Molecular and biosynthetic heterogeneity of fucosyl glycoproteins associated with rat brain synaptic functions.

The composition and biosynthesis of fucosyl glycoproteins present in rat brain synaptic membranes and synaptic junctions were investigated. Reaction with 125I-labelled fucose-binding protein (Lotus tetragonolobus) following sodium dodecyl sulphate gel electrophoresis identified 6--8 fucosyl glycoproteins in synaptic membranes but only three major high molecular classes (Mr = 180 000, 130 000 and 110 000) in synaptic junctions. Affinity chromatography on concanavalin A-Sepharose resolved each of the synaptic junctional fucosyl glycoproteins into concanavalin A-positive and negative components indicating the presence of at least six high molecular weight fucosyl glycoproteins in synaptic junctions. Following the administration of [3H]fucose synaptic membranes, synaptic junctions and post-synaptic densities incorporated isotope, the order of relative specific activities being synaptic membranes greater than synaptic junctions greater than post-synaptic densities. Fractionation of [3H]fucose-labelled synaptic junctions on concanavalin A-Sepharose revealed a time-dependent increase in the percentage of isotope associated with the concanavalin A-positive glycoproteins. The results demonstrate both molecular and biosynthetic heterogeneity of fucosyl glycoproteins associated with synaptic junctions.