Distribution of membrane glycoproteins among the organelles of a single identified neuron of aplysia. I. association of a [H]glycoprotein with vesicles

[³H]-acetylgalactosamine injected into the cell body of R2, the giant cholinergic neuron in the abdominal ganglion, is rapidly incorporated into membrane glycoprotein and glycolipid. Incorporation, which is localized to the injected cells, occurs at a constant rate for approximately 15 h. By that time, 83% of the labeled macromolecules are associated with membranes. Quantitative electron microscopic radioautography of the cell body shows that labeling of membranous organelles is selective: the Golgi apparatus, endoplasmic reticulum, and lucent and compound vesicles are labeled, while the nucleus, end-stage lysosomes, and mitochondria are not. SDS-polyacrylamide gel electrophoresis of the total membranes from more than 40 R2s examined individually resolves reproducibly 5 major labeled glycoprotein components. In order to determine which of these are associated with vesicles, we isolated a labeled vesicle fraction from R2 using a combination of differential centrifugation and filtration on a column of glass beads with 200 nm pores. This fraction was consistently enriched in [³H]glycoproteins I (180,000 Daltons) and V (90,000 Daltons) relative to those fractions containing larger organelles. These experiments suggest that different organelles contain characteristic membrane components.