The turnover of the lipid components of myelin

The rate of loss of radioactivity in the lipid components of rat myelin labeled with acetate‐1‐C 14 was determined over a period of one year. Rats were injected with acetate‐1‐C 14 at 15舑16 days of age and purified myelin was prepared by differential ultracentrifugation from brain and spinal cord of this group at 1 day, 2 weeks, 1 month, 2 months, 3 months, 6 months and 1 year after injection. Total lipid was extracted from the myelin preparations and the lipids were separated into their components by thin‐layer chromatography. Cholesterol, galactolipid, ethanolamine phosphatide, choline phosphatide, inositol phosphatide, serine phosphatide and sphingomyelin specific activities at each age were measured. Three of the myelin lipid components, serine phosphatide, inositol phosphatide, and choline phosphatide decreased in specific activity faster than cerebroside, cholesterol, sphingomyelin, and ethanolamine phosphatide. Acetate‐1‐C 14 injected into adult animals, though incorporated into myelin to a very small extent, is taken up primarly in the choline phosphatide. These experiments suggests that myelin does not behave as a fixed entity but that certain constituents may be more actively metabolized than others.