Kinetics of Entry of P0 Protein into Peripheral Nerve Myelin

Abstract: Sciatic nerves from 9-day-old rat pups were removed, sliced into 0.4-mm sections, and incubated with ³H]fucose or ¹⁴C]glycine precursors. The nerve slice system gave nearly linear incorporation of ³H]fucose as a function of time for 3 h, after an initial lag of ?30 min for homogenate and ?60 min for myelin. Incorporation of ³H]fucose at constant specific radioactivity was directly proportional to exogenous fucose levels over the range 3.0 × 10^?8 m to 1.5 × 10^?6 m . Analysis of labeled proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that greater than 50% of labeled glycoprotein was P₀, with no other major constituents. This system was used in fucose-chase experiments to determine that a period of ?20 min elapses between fucosylation and assembly of P₀ into myelin. Cycloheximide inhibition of protein synthesis was used to determine that a period of ?33 min elapses between protein synthesis and appearance of P₀ myelin.