A TRUNCATED EPOXY GLUCOSYLCERAMIDE UNCOUPLES GLYCOSPHINGOLIPID BIOSYNTHESIS BY DECREASING LACTOSYLCERAMIDE SYNTHASE ACTIVITY

Introduction of an epoxide function at the C4 position of the glucose moiety of a truncated glucosylceramide (GlcCer) yields two stereoisomeric products namely a gluco- and a galacto-derivative. The effects of both analogues on the [C-14]serine incorporation into glycosphingolipids as well as on lactosylceramide (LacCer) synthase activity of primary cultured neurons derived from the telencephalon of 8-day-old chick embryos were investigated. Whereas the galacto-derivative had no effect either on the pattern of labeled glycosphingolipids or on LacCer synthase activity, pretreatment (24 h) of neurons with the gluco derivative caused a concentration dependent (IC50 = 8 mu M) and irreversible decrease of the specific activity of LacCer synthase. As a consequence the biosynthetic glycosphingolipid pattern of cultured neurons treated with the glucoanalogue changed as follows: the radioactive label of all glycosphingolipids biosynthetically derived from GlcCer was decreased while labeling of GlcCer increased significantly. The inhibitory effect of the gluco derivative on LacCer synthase activity was much less pronounced in vitro. Thus 250 mu M analogue caused only about 30% inhibition of enzymatic activity.