METABOLISM OF EXOGENOUS GANGLIOSIDE GM1 IN CULTURED CEREBELLAR GRANULE CELLS - THE FATTY-ACID AND SPHINGOSINE MOIETIES FORMED DURING DEGRADATION ARE RE-USED FOR LIPID BIOSYNTHESIS

Cerebellar granule cells, differentiated in vitro, were parallelly fed with [Sph-H-3]GM1 and [stearoyl-C-14]GM1, under identical conditions (10(-6) M ganglioside; pulse, from 1-4 h; chase, up to 24 h after 4 h pulse) and the salvage pathways of sphingosine and stearic acid were i nvestigated. It was observed that both sphingosine and stearic acid, l iberated during the intralysosomal degradation of ganglioside, are met abolically recycled, along distinct pathways. Sphingosine is used for the biosynthesis of a number of sphingolipids, particularly ceramide, glucosyl-ceramide, gangliosides and sphingomyelin; stearic acid is uti lized for the biosynthesis of sphingolipids, and to a greater extent, glycero-phospholipids, especially those endogenously richer in stearic acid (phosphatidyl-ethanolamine and phosphatidyl-choline). No evidenc e was provided for a salvage pathway for ceramide.