Conversion of dihydroceramide to ceramide occurs at the cytosolic face of the endoplasmic reticulum.
Dihydroceramide desaturase is responsible for the introduction of the 4,5-trans double bond into ceramide. Here, we describe the localization of this enzyme in the endoplasmic reticulum (ER) using ER- and Golgi-enriched fractions from rat liver. Furthermore, enzyme topology was studied. Mild proteolysis of ER-derived vesicles under conditions which assure membrane integrity (latency of mannose 6-phosphatase was at least 91%) resulted in an up to 90% inactivation of dihydroceramide desaturase activity. This indicates a cytosolic orientation of dihydroceramide desaturase activity in the ER membrane.
Michel
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Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Germany.
van Echten-Deckert
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D000818:Animals; D002518:Ceramides / Q000737:chemistry / Q000378:metabolism*; D003600:Cytosol; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D005952:Glucose-6-Phosphatase / Q000378:metabolism; D006056:Golgi Apparatus / Q000201:enzymology*; D008099:Liver / Q000201:enzymology*; D010088:Oxidoreductases / Q000378:metabolism*; D011402:Pronase / Q000378:metabolism; D051381:Rats; D012799:Sialyltransferases / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
D002518:Ceramides; D010088:Oxidoreductases; C108138:dihydroceramide desaturase; D012799:Sialyltransferases; C019916:CMP-N-acetylneuraminic acid-monosialoganglioside sialyltransferase; D005952:Glucose-6-Phosphatase; D014357:Trypsin; D011402:Pronase