Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.4.1 (phosphodiesterase)
 18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The subcellular distributions of the enzymes which synthesise sphingomyelin (SM) and glucosylceramide (GluCer) from ceramide have been assessed in BHK cells. On a sucrose density gradient GluCer synthase (a marker of the cis/medial Golgi apparatus) and the trans-Golgi marker galactosyltransferase showed an similar monotonic distribution. In contrast, SM synthase showed two peaks of activity, a minor one which migrated with the Golgi markers and a major one which had a density close to that of plasma membrane markers (sphingomyelin, cholesterol, PtdSer, ganglioside GM3 and alkaline phosphodiesterase). When cell homogenates were treated with digitonin, the sedimentation characteristics of the Golgi markers was largely unaffected whereas the plasma membrane markers and the main peak of SM synthase activity were shifted to higher density. In contrast, when cells were treated with brefeldin A (BFA) the Golgi markers were shifted to higher density but not the plasma membrane markers or the main peak of SM synthase. These results suggest that the bulk of SM synthase activity in BHK cells is not associated with the Golgi cisternae but with a cell compartment which is relatively rich in cholesterol (e.g., plasma membrane, endosomes or trans-Golgi network.) Further experiments in which cells were treated with sphingomyelinase provided evidence that SM synthase activity was in an internal compartment and not at the plasma membrane.
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PMID:The subcellular sites of sphingomyelin synthesis in BHK cells. 939 80

BHK cells either untreated or infected with Semliki Forest virus have been fractionated on sucrose density gradients. Virus infection caused an increase in density of a membrane fraction enriched in sphingomyelin (SM), cholesterol, SM synthase and sialyltransferase activity. This increase in density was related to incorporation of viral proteins into this fraction, which is likely to contain trans-Golgi network (TGN) membranes. In contrast, glucosylceramide synthase and galactosyltransferase activities (markers for cis/medial and trans-Golgi respectively) underwent no density shift and alkaline phosphodiesterase, a plasma membrane marker, was only slightly density-shifted in infected cells. When cells were incubated with NBD-ceramide to enable them to synthesise NBD-SM and then washed with albumin to remove surface label, fluorescence in untreated cells was concentrated in a single juxtanuclear spot but in infected cells this region of bright fluorescence was larger and extended around the nucleus. After fractionation of these cells, NBD-SM (but only a small proportion of the NBD-ceramide) was found to be shifted into the higher density fraction in infected cells. This work provides further evidence that SM synthase is not mainly localised in the early Golgi cisternae as previously thought, but is associated more with a cholesterol-rich compartment which could be the TGN.
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PMID:Enzyme distributions in subcellular fractions of BHK cells infected with Semliki forest virus: evidence for a major fraction of sphingomyelin synthase in the trans-golgi network. 1039 39