Intracellular Translocation of Myelin Proteolipid Protein

: Brainstem slices prepared from 22‐day‐old rats, were employed to study the intracellular translocation of radioactively labeled myelin proteolipid protein (PLP). Double‐isotope and short pulse‐chase procedures allowed us to demonstrate the flux of PLP through nine different subcellular membrane fractions that were isolated on the basis of their particle size and buoyant density. Tagged PLP was rapidly depleted from microsomes, showed transient passage through a number of presumably intermediate membranous pools, and accumulated in myelin. On the basis of the kinetics of PLP labeling and isotope ratios, the membranes can be arranged as they participate in the intracellular translocation of PLP and consistently show a pattern indicating possible precursor‐product relationships.