Incorporation rate of GM1 ganglioside into mouse brain myelin: effect of aging and modification by hormones and other compounds.

The turnover rate of GM1 ganglioside in myelin was examined reveal age-related alterations in the metabolic activity. Three different age groups of mice were given deuterium oxide, and myelin was prepared from cerebella at intervals of two weeks. GM1 was isolated from the total myelin gangliosides by high performance liquid chromatography. Deuterated sugar moieties of GM1 were determined by chemical ionization-mass spectrometry which provided prominent quasimolecular ions. This method made it possible to determine separately the incorporation of deuterium into internal and external galactoses as well as other components. The incorporation rate of GM1 into myelin was clearly shown to be decreased with advancing age. Lower incorporation of newly synthesized sialic acid into GM1 than that of other sugars may indicate reutilization of sialic acid at about 50%. The possibility of modification of the myelin metabolism by exogenous factors was examined by monitoring the incorporation rate of GM1 in animals treated with chemical agents. It was revealed that thyroxine enhanced the incorporation of GM1 into adult brain myelin, whereas propylthiouracil reduced the incorporation. Other chemicals, estradiol, S-adenosylmethionine and LM1 ganglioside, showed only minor effects on the myelin turnover.