Occurrence of glycosylation and deglycosylation of exogenously administered ganglioside GM1 in mouse liver

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Abstract
Ganglioside GM1, 3H-labeled at the level of terminal galactose or sphingosine, was i.v. injected into Swiss albino mice and some steps in its metabolic fate in the liver were investigated. After administration of [3H]sphingosine-labeled Gm1 all major liver gangliosides [GM3, GM2, GM1, GD1a-(NeuAc,NeuG1)] became radioactive, the radioactivity residing in all cases on the sphingosine moiety. The specific radioactivity was highest in GM1, which carried .apprx. 53% of the radioactivity incorporated into gangliosides, followed by GM2, with 34.5% of incorporated radioactivity, GM3 and GD1a-(NeuAc,NeuG1), both with .apprx. 5% of incorproated radioactivity. After administration of [3H]galactose-labeled GM1 the only radioactive gangliosides present in the liver were GM1 and GD1a-(NeuAc,NeuG1), the former carrying .apprx. 95% of the total ganglioside-incorproated radioactivity, the latter .apprx. 3%. Both gangliosides were radioactive exclusively in the terminal galactose residue. According to these results exogenously administered GM1, after being taken up by the liver, is mainly degraded to GM2 and GM3, a part being, however, sialylated to GD1a-(NeuAc,NeuG1). Exogenous GM1 may be involved in the metabolic routes of endogenous liver gangliosides.

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