Metabolism of three subfractions of myelin in developing rats.

Abstract

Abstract Purified myelin, isolated from rat brain, was subfractionated into light, medium and heavy myelin. The metabolism of [3H] leucine in myelin subfractions was studied at intervals from 1 to 24 hours and from 18 hours to 85 days after the injection of 12-day-old rats. The metabolism of [14C] glucose in myelin subfractions was also examined during the 85 day interval. In addition, the development of each of these subfractions, as reflected by protein accretion, was determined. Between 13 and 97 days of age, the amount of the three myelin subfractions increased 10- to 44-fold. At 13 days of age the heavy subfraction accounted for the greatest percentage of myelin protein. However, beyond 13 days, light myelin predominated. The total 3H-radioactivity in the light, medium and heavy subfractions increased throughout most of the 85 day interval examined. The 3H specific radioactivity (3H dpm/μgram protein) of light myelin peaked at 12 hours after injection. The specific radioactivity of both 3H and 14C (14C dpm/μgram lipid) in light myelin declined beyond the initial time point in the long term (18 hour – 85 day) study. In contrast, the specific radioactivity of both 3H and 14C peaked in the medium and heavy subfractions at 4 days after injection of radioactive precursor. The possible existence of a membranous precursor to myelin is discussed.