Neutral lipid precursors for gangliosides are not formed by rat liver homogenates or by purified cell fractions.

As part of an ongoing investigation into the ganglioside and neutral glycosphingolipid biosynthetic pathways in rodent liver, the synthesis of ceramide, glucosylceramide and lactosylceramide was examined in homogenates and purified membrane fractions of rat liver. Ceramide synthesis and its stimulation by exogenously added D-sphingosine was demonstrated in homogenates and isolated membrane fractions, with activity concentrated in the endoplasmic reticulum. In contrast, significant D-sphingosine- or ceramide-dependent formation of glucosylceramide, or glucosylceramide-dependent formation of lactosylceramide (in the presence of labelled UDP-[14C]glucose and UDP-[14C]galactose, respectively,) could not be demonstrated. The possibility is raised that liver may be dependent on extra-hepatic sources of neutral glycosphingolipids to support ganglioside biosynthesis.