Salvage of catabolic products in ganglioside metabolism: a study on rat cerebellar granule cells in culture

Abstract

Cerebellar granule cells in culture were subjected to a pulse (0.5–4 h)-chase (0–4 h) of 10⁻⁶ M [³H]ganglioside GM1 carrying the radioactive label at the level of NeuAc ([³H-NeuAc]GM1), Sph ([³H-Sph]GM1) or Gal ([³H-GallGMl) and the formed [³H]metabolites were determined. With all forms of [³H]GM1, there was formation of [³H]catabolites, including [³H]H₂O and [³H]biosynthetic products obtained by recycling of [³H]NeuAc, [³H]Sph and [³H]Gal released during intralysosomal ganglioside degradation (salvage processes). Much higher amounts of [³MH₂O were produced from [³H-Gal]GM1 than [³H-Sph]GM1 and [³H-NeuAc]GM1; conversely, more products from salvage processes (polysialogangliosides GD1a, GDlb, GTlb, O-acetylated GT1b, protein-bound radioactivity) were obtained with [³H-NeuAc]GM1; than the two other forms of [³H]GM1, Liberated [³H]NeuAc produced 10-fold less tritiated water and 10-fold higher salvage products than [³H]Gal. Using [³H-NeuAc]GM1; granule cells appeared to metabolize 7.7% of membrane-incorporated exogenous GM1 per hour with a high degree of NeuAc recycling and the calculated metabolic half-life was 6.5 h.