Incorporation of L-[3H]fucose into glycoproteins was studied in R2, the giant neuron in the abdominal ganglion of Aplysia. [3H]fucose injected directly into the cell body of R2 was readily incorporated into glycoproteins which, as shown by autoradiography, were confined almost entirely to the injected neuron. Within 4 h after injection, 67% of the radioactivity in R2 had been incorporated into glycoproteins; at least 95% of these could be sedimented by centrifugation at 105,000 g, suggesting that they are associated with membranes. Extraction of the particulate fraction with sodium dodecyl sulfate (SDS), followed by gel filtration on Sephadex G-200 and polyacrylamide gel electrophoresis in SDS revealed the presence of only five major radioactive glycoprotein components which ranged in apparent molecular weight from 100,000 to 200,000 daltons. Similar results were obtained after intrasomatic injection of [3H]N-acetylgalactosamine. Mild acid hydrolysis of particulate fractions released all of the radioactivity in the form of fucose. When ganglia were incubated in the presence of [3H]fucose, radioactivity was preferentially incorporated into glial cells and connective tissue. In contrast to the relatively simple electrophoretic patterns obtained from cells injected with [3H]fucose, gel profiles of particulate fractions labeled with [14C]valine were much more complex.
Increasing amounts of glycoprotein synthesized from L-[3H]fucose injected into the cell body of R2, an identified Aplysia neuron, were found in the right pleuro-abdominal connective. Autoradiography revealed that the glycoproteins were localized in the axon of R2. Glycoproteins appearing in the axon presumably were synthesized in the cell body, since no significant incorporation was observed when [3H]fucose was injected directly into the axon. [3H]glycoproteins were detected in the connective after a delay of 1 h after intrasomatic injection. Thereafter, transport from the cell body was rapid, and by 10 h after injection, 45% of the total neuronal [3H]glycoprotein had appeared in the axon. By analysing the radioactivity in cell body and connective 4, 10, and 15 h after injection, we found that [3H]glycoproteins were transported selectively compared to nonmacromolecular material. Sequential sectioning of the connective revealed that [3H]glycoproteins were transported in discrete waves. The population of membrane-associated [3H]glycoproteins in the axon differed from that in the cell body. Two of the five somatic components appeared to be transported preferentially. In addition a new component appeared in the axon 10 h after injection.