Abstract
Abstract Through the use of a sensitive and specific gas chromatographic assay, the concentration of monogalactosyl diglyceride has been measured in whole brain and in fractions of brain from rats of varying age. The concentration of monogalactosyl diglyceride in whole brain was barely measurable before 10 days of age; increased sharply especially after 16 days up to about 20 days of age; and then decreased rather quickly to adult values. In adult brain, most of the monogalactosyl diglyceride was associated with myelin (64 to 68%); the next highest amount (15 to 18%) was recoverable from the microsomal fractions. In brains undergoing active myelination the greater part of the monogalactosyl diglyceride appeared in the microsomal fraction up to the age of 20 days. After 20 days the quantity of the galactosyl diglyceride decreased precipitously in the microsomal fraction, and increased sharply in the small myelin fraction. In the actively myelinating brain very little monogalactosyl diglyceride is found in the large myelin fraction; however in adult brain there are equal amounts in the small and large myelin fractions. Thus the galactosyl lipid is associated with an increasingly larger particle as the animal ages into adulthood. The enzyme activity responsible for the biosynthesis of the galactosyl diglyceride resided almost exclusively (88% of total) in the microsomal fraction. These data indicate that a temporal relationship exists between the site of synthesis (microsomal) and site of deposition (myelin) of monogalactosyl diglyceride. This suggestion was confirmed by the finding that the specific radioactivity of monogalactosyl diglyceride in myelin from 23-day-old rats was the same as the specific radioactivity of monogalactosyl diglyceride derived from the microsomal fraction of brain from 20-day-old rats.
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