The c-series gangliosides GT3, GT2 and GP1C are formed in rat liver Golgi by the same set of glycosyltransferases that catalyse the biosynthesis of asialo-, a- and b-series gangliosides
Biosynthesis of the c-series gangliosides GT3, GT2 and GP1c was studied in Golgi derived from rat liver. Competition experiments show that the synthesis of ganglioside GT2 (GalNAcβ1→4-(NeuAcα2→8NeuAcα2→3) Gal-β1→4Glcβ1→1Cer)from GT3 (NeuAcα2→8Neuacα2→8Neuacα2→3Galβ1→4Glcβ1→1Cer)seems to be catalysed by the same N-acetylgalactosaminyl-transferase (GalNAc-T), which converts GM3(NeuAcα2→3Galβ1→4Glcβ1→1Cer) to GM2 (GalNAcβ1-4(NeuAcα2→3) Galβ1→4Glcβ1→1Cer) Similar competition experiments suggest moreover that the sialytransferase V (SAT V), which catalyses the synthesis of GT1a (NeuAcα2→3Galβ1→3GalNAcβ1→4 (NeuAcα2→3)-Galβ1→4Glcβ1→1Cer) from GD1a (NeuAcα→2→3Galβ1→(NeuAcα2→3) Galβ1→4Glcβ1→1 Cer) appears to be identical to the enzyme that catalyses the synthesis of GP1c (NeuAcα2→3Galβ1→3GalNAcβ1→4(NeuAcα2→3) Galβ1→4Glcβ1→1→Cer) appears to be identical to the enzyme that catalyses the synthesis of GPIC (NeuAcα2→8NeuAcα2→3Galβ1→3GalNacβ1→ (NeuAcα2→8NeuAcα2→8NeuACα2→3) Galβ1→4 Glcβ1→1 Cer). OUr experiments also suggest that SAT V also catalyses the synthesis of GT3(NeuAcα2→8NeuAcα2→8NeuAcα2→3Galβ1→4Glcβ1→1Cer) from GD3 (NeuAcα2→8NeuAcα2→3Galβ1→4Glcβ1→1Cer. These results are integrated into our model for ganglioside biosynthesis and its regulation.