The degradation of
oligosaccharide-diphospho-
dolichol leads to the release of
oligosaccharide material ranging from (Glc)3(Man)9(GlcNAc)2-P to (Man)3 species and further smaller species. The subcellular location of the
glucosidases and
mannosidases involved in this catabolic process has been investigated on the basis of their differential sensitivity towards specific inhibitors (
castanospermine, deoxymannojirimycin and
swainsonine). The results indicate that the first steps of degradation down to the (Man)6 species occurs in the rough endoplasmic reticulum. This result is supported by the fact that the (Man)6 species is the end product when
lipid-intermediate-derived glucosylated
oligosaccharides are incubated with purified rough endoplasmic reticulum membranes.
Swainsonine and lysosomotropic agents (
chloroquine and
ammonium chloride) do not affect the degradation process, thus indicating that neither Golgi apparatus nor lysosomes are involved in this catabolism. The observation of the same degradation pattern of the released
oligosaccharide material in
mannosidosis fibroblasts, lacking lysosomal
mannosidases, confirms these results. Finally, the subcellular distribution of the released
oligosaccharide material indicates that the
oligomannosides larger than (Man)6 species are sequestered in the particulate fraction whereas, in contrast,
oligomannosides smaller than (Man)6 species are found predominantly in the cytosol. Taken altogether, the experiments demonstrate that the first steps of the degradation of
oligosaccharide-diphospho-
dolichol occurs in the rough endoplasmic reticulum producing
oligomannosides of the (Man)6 species which are then translocated to the cytoplasm to be further degraded.