Change in a myelin-associated glycoprotein in rat brain during development: metabolic aspects.

The higher apparent molecular weight of the newly synthesized glycoprotein in immature rat myelin in comparison with that in mature myelin, which was originally demonstrated with radioactive fucose, was also shown by double labeling experiments with radioactive glucosamine or N-acetylmannosamine. In addition, periodic acid-Schiff staining of gels, on which the glycoproteins of mature and immature myelin were electrophoresed separately or mixed together, revealed that the stained glycoprotein in immature myelin had a higher apparent molecular weight. Age studies with radioactive fucose showed that the greatest difference in the apparent molecular weight of the newly synthesized glycoprotein occurred at 12 days. The magnitude of the difference decreased gradually with age until 25 days when the glycoprotein electrophoresed to the same position as that in more mature myelin. Long-term experiments, in which 12- or 13-day-old rats were injected with radioactive fucose and allowed to survive for varying periods of time before myelin isolation, also revealed a gradual decrease with age in the extent of the shift of the glycoprotein toward a higher molecular weight. The possible significance of the developmental change in the glycoprotein for the process of myelin formation is discussed.