Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.99.7 (sialyltransferase)
 1,534 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Six naturally occurring and three synthetic molecular species of lactosylceramide (LacCer) were used to examine the molecular species specificity of CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase in a Golgi-rich fraction of rat liver. The enzyme molecular species specificity was determined either in the presence of nonspecific lipid transfer protein or in the presence of detergents. Assays performed in the presence of transfer protein showed that for those lactosylceramide molecular species with either d18:1 or d18:0 long chain base the enzyme activity decreased linearly as the effective carbon number of the fatty acid increased. An increase in the carbon number of the long chain base decreased the activity of the enzyme twice as much as a corresponding increase in the carbon number of the fatty acid. On the other hand, when the enzyme activity was assayed in the presence of detergents, there was no significant difference in activity among the various molecular species of lactosylceramide based upon the carbon number of the fatty acid or on the presence of a double bond in the long chain base. However, the decrease in enzyme activity with an increase in the carbon number of the long chain base persisted. These results demonstrate that sialyltransferase has binding specificity with respect to the long chain base, but not the fatty acid. The apparent molecular species towards the fatty acid is related to the aqueous solubility of the various LacCer molecular species.
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PMID:Lactosylceramide molecular species specificity of rat liver CMP-N-acetylneuraminate:lactosylceramide sialyltransferase. 261 78

CMP-N-acetylneuraminate:lactosylceramide alpha-2,3-sialyltransferase is tightly associated with the luminal side of the Golgi membrane as is its lipid substrate, lactosylceramide. In order to understand the kinetics, properties, and regulation of this enzyme, it is necessary to alter the amount and type of substrate in the membrane while minimizing changes in the membrane environment or in the conformation of the enzyme. Therefore, nonspecific lipid transfer protein, which accelerates the transfer of phospholipids, cholesterol, and glycosphingolipids between membranes was used to study the properties and kinetics of rat liver CMP-N-acetylneuraminate:lactosylceramide sialyltransferase. These results are compared to those obtained in parallel experiments using detergent-solubilized substrate. Enzyme activity was increased four- to fivefold by transfer protein and was consistently higher than the activity measured in the presence of detergents. In contrast to the results obtained with detergents, the enzyme activity increased linearly with both Golgi protein and with incubation time for up to 60 min. The Km values for the water-soluble substrate, CMP-neuraminic acid, were virtually identical when determined in the presence of transfer protein (0.23 mM) or detergents (0.27 mM). On the other hand, the apparent Km values for the lipophilic substrate, lactosylceramide, were markedly different when determined in the presence of transfer protein (47.9 microM) or in the presence of detergents (1.2 microM). These observations suggest that transfer protein is a useful tool to study the properties and kinetics of membrane-bound enzymes when both the enzyme and substrate are components of the same membrane.
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PMID:Nonspecific lipid transfer protein in the assay of a membrane-bound enzyme CMP-N-acetyl-neuraminate:lactosylceramide sialyltransferase. 335 52

It has previously been shown that when the molecular species specificity of rat liver Golgi CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase was determined, using as the substrate lactosylceramide (LacCer) incorporated into liposomes prepared with rat liver Golgi lipids, the enzyme showed a pronounced variation in activity towards the various molecular species of LacCer (J. Lipid Res. 1989. 30: 1789-1797). In this paper, -the LacCer molecular species specificity of sialyltransferase from neuroblastoma NB2a cells was examined using five naturally occurring and three synthetic molecular species of LacCer. The enzyme activity was determined by following the formation of [14C]GM3 from CMP-[14C]neuraminic acid and individual molecular species of LacCer incorporated into liposomes. Nonspecific lipid transfer protein was included in the enzyme assay to facilitate the transfer of LacCer and other lipids between the liposomes and the membrane where sialyltransferase is located. In these enzyme assays the liposomes contained approximately 10 times more lipid phosphorus than either the microsomal fraction of NB2a cells or the Golgi fraction of rat liver. Thus, in the presence of nonspecific lipid transfer protein, the lipid composition of the membrane where sialyltransferase is located was modified to resemble the lipid composition of the liposomes. When the molecular species specificity of NB2a cell sialyltransferase was determined with LacCer incorporated into liposomes prepared with NB2a cell lipids, the enzyme showed no specificity towards the various molecular species of LacCer. However, when the molecular species specificity of NB2a cell sialyltransferase was determined with LacCer incorporated into liposomes prepared with rat liver Golgi lipids, the enzyme showed a variation in activity towards the various LacCer molecular species similar to that observed with the liver Golgi enzyme using liposomes prepared with liver Golgi lipids. Likewise, when the molecular species specificity of rat liver Golgi sialyltransferase was determined with LacCer incorporated into liposomes prepared with NB2a cell lipids, the liver enzyme then showed no specificity towards the various molecular species of LacCer. These results indicate that the lipid environment of the membrane can alter the molecular species specificity of sialyltransferase towards its lipid substrate, LacCer.
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PMID:Effect of membrane lipids on the lactosylceramide molecular species specificity of CMP-N-acetylneuraminate:lactosylceramide sialyltransferase. 835 56