Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

CMP-sialic acid:GM3 sialyltransferase (GD3 synthase; EC 2.4.99.8) was characterized in a membrane-enriched preparation (P2 pellet) from mouse embryos at embryonic day 12 (E-12). Gangliosides GD3 and GM3 were the major radiolabeled products of the reaction. Optimum GD3 synthase activity was obtained at pH 6.0 using 0.1% detergent Triton CF-54. The Km values for GM3 and CMP-sialic acid were 55 and 80 microM, respectively. The Vmax value was calculated as 622 pmol/mg protein/hr. Ganglioside GD3, as end product, induced a two-step reduction of enzyme activity in the range of concentrations from 0 to 34 microM (40%) and from 150 to 300 microM (65%). The rate of GD3 formation was similar in whole embryos and in embryo head and body regions. GD3 synthase activity in tw1/tw1 mutant mouse embryos, which express defects in neuronal differentiation, was only 40% of that in normal wild-type (+/+) embryos. Enzyme activity in heterozygous (+/twl) embryos was similar to that in +/+ embryos. These findings suggest that the reduced GD3 synthase activity in the mutants might arise as a consequence of failed nervous system development and might reflect a secondary rather than a primary effect of the mutation.
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PMID:Ganglioside GD3 biosynthesis in normal and mutant mouse embryos. 182 26

The acceptor specificities of four sialytransferases (I, II, IV and V) involved in ganglioside biosynthesis were studied in Golgi vesicles derived from rat liver. The activities of these sialytransferases were strongly detergent-dependent. Competition experiments with different detergent concentrations using LacCer (Gal beta 1----4Glc beta 1----1Cer), GM1a [Gal beta 1----3GalNAc beta 1----4(NeuAc alpha 2----3)Gal beta 1----4Glc beta 1----1Cer] and GD1b [Gal beta 1----3GalNAc beta 1----4(NeuAc alpha 2----8NeuAc alpha 2----3)Gal beta 1----4Glc beta 1----1Cer] as substrates, and as mutual inhibitors for ganglioside sialyltransferase activity, suggested that sialyltransferase IV was able to catalyze the sialyltransfer in alpha 2----3 linkage to the galactose residues of LacCer as well as of GM1a and GD1b. The other three sialyltransferases (I, II and V) seemed to be quite specific for their respective glycolipid acceptors, LacCer, GM3 and GM1b, GD1a and GT1b. Furthermore the kinetic data showed that sialyltransferase I was inactive at higher detergent concentrations (greater than 75 micrograms Triton CF-54); under these conditions, formation of GM3 and GD1a was catalyzed only by sialyltransferase IV. These results have been integrated into a model for ganglioside biosynthesis and its regulation.
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PMID:Substrate specificity of alpha 2----3-sialyltransferases in ganglioside biosynthesis of rat liver golgi. 199 63

Lauryldimethylamine oxide (LDAO) was employed in the purification of the GM3 ganglioside forming enzyme, CMP-sialic acid:lactosylceramide alpha 2-3 sialyltransferase (SAT-1) (4). This detergent has advantages over the typically employed Triton detergents in the solubilization and stabilization of this sialyltransferase. Crude protein fractions solubilized from rat liver Golgi by several such detergents are very similar in composition as determined by two-dimensional gel electrophoresis. However, LDAO appears to activate and stabilize SAT-1 activity. It is possible that SAT-1 activation involves the structurally similar hydrophobic moieties and quaternary amino groups of LDAO and phosphatidylcholine.
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PMID:Special considerations in the purification of the GM3 ganglioside forming enzyme, CMP-sialic acid:lactosylceramide alpha 2-3 sialyltransferase (SAT-1): solubilization of SAT-1 with lauryldimethylamine oxide. 222 67

An alpha 2----3 glycolipid galactosyl sialyltransferase (SAT3/4) has been partially purified from embryonic chicken skeletal muscle. It is preserved in 50 mM Hepes buffer (pH 6.8) containing 1% Triton CF-54 and 20% glycerol at -70 degrees C for a period of 6 months without loss of activity. The SAT3+4 preparation transfers sialic acid to nLcOse4Cer, nLcOse6Cer and GgOse4Cer with respective Km values of 1.4, 0.83 and 0.45 mM. The activity is stimulated 2-3-fold at high substrate concentration and 6-8-fold at low substrate concentration; 0.01 and 0.005 mumol for asialo GM1 and 0.025 and 0.01 mumol for other glycolipids in the presence of phosphatidylcholine (PC) and sphingomyelin (SM) at an optimum concentration 0.75%. A higher concentration is inhibitory. SM from chicken muscle is more effective than that from bovine brain and the stimulation is qualitatively proportional to that of the saturated fatty acyl content of SM. Free fatty acids (palmitic and stearic), their sodium salts, other choline compounds including choline chloride, phosphorylcholine and acetylcholine either do not have any effect or are inhibitory. Acetylcholine, even in the presence of SM and PC, is strongly inhibitory (70%).
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PMID:Biosynthesis of GM1b and similar neolactoseries gangliosides by a partially purified chicken skeletal muscle sialyltransferase. Effect of sphingomyelin and acetylcholine. 222 21

A CMP-NeuAc:GM1 alpha 2-3 sialyltransferase (GD1a synthase, 2.4.99.2) has been purified from the Triton extract of rat brain. The enzyme was purified and resolved by affinity chromatography on CDP-Sepharose column by a linear NaCl gradient elution. Final purification was achieved by elution from a 'GM1-acid'-Sepharose column. SDS-PAGE of the enzyme revealed a single protein band with an apparent Mr 44 kDa. It catalyzed specifically the sialylation of GD1b, GM1 and asialo-GM1. Enzyme products were identified by TLC in three different solvent systems. The Km value for GM1 was 7.5 x 10(-2) M, and for CMP-NeuAc it was 6.5 x 10(-5) M.
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PMID:Purification and characterization of CMP-NeuAc:GM1 (Gal beta 1-4GalNAc) alpha 2-3 sialyltransferase from rat brain. 226 6

A simple and rapid procedure using anion exchange chromatography was established for determinations of the activity of ganglioside GD3 synthase (CMP-NeuAc: GM3, alpha 2----8 sialyltransferase) which catalyzes the conversion of ganglioside GM3 to GD3. The procedure was applicable for determination of activity of other ganglioside synthases. With the use of this procedure and GM3-acid affinity chromatography, the GD3 synthase was partially purified about 80 fold from a Lubrol PX extract of rat liver Golgi apparatus. The enzyme obtained had a pll optimum of 6.4. The preferred acceptors of the enzyme was GM3 containing N-acetylneuraminic acid (GM3 (NeuAc)) and GM3 containing N-glycolylneuraminic acid (GM3 (NeuGc)), with 2-fold higher V max in the latter than in the former. The Km values for GM3 (NeuAc), GM3 (NeuGc) and CMPNeuAc were 0.7 mM, 0.11 mM and 75 microM, respectively. The reaction product was identified as GD3 by thin layer chromatography. As to detergent, this enzyme showed maximum activity in 0.3% of Triton CF-54. The synthase did not require divalent cations for the activity, but rather Zn2+ and Cd2+ at 5 mM completely inhibited the enzyme activity. Cytidine nucleotides were strong inhibitors. The product, GD3, at 2 mM inhibited 30% the enzyme activity. The activity level of the GD3 synthase of rat liver was markedly different in rat strains, WKAH and TO strains being highest among eight strains examined. Male rat exhibited higher level than female. The synthase activity in rat liver was high at neonatal stage and decreased gradually thereafter.
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PMID:[A study of partial purification of ganglioside GD3 synthase and its enzymatic properties]. 232 44

The pathway for synthesis of three glycosphingolipids bearing a common sialyl-Lex determinant (NeuAc alpha 2----3Gal beta 1----4[Fuc alpha 1----3]GlcNac beta 1----R) from their type 2 lactoseries precursors has been studied using the 0.2% Triton X-100-soluble fraction from human lung carcinoma PC9 cells. Two enzymes were found to be required for their synthesis: (i) an alpha 1----3 fucosyltransferase, the properties of which have been characterized as being similar to the enzyme from human small cell lung carcinoma NCI-H69 cells (Holmes, E. H., Ostrander, G. K., and Hakomori, S. (1985) J. Biol. Chem. 260, 7619-7627); and (ii) an alpha 2----3 sialyltransferase that was efficiently solubilized by 0.2% Triton X-100 and required divalent metal ions and 0.3% Triton CF-54 for optimal activity at pH 5.9 in cacodylate buffer. Biosynthesis of the sialyl-Lex determinant was shown to proceed via sialylation of nLc6 and nLc4, followed by alpha 1----3 fucosylation at the penultimate GlcNAc residues, based on the following: (i) transfer of NeuAc by PC9 cell sialyltransferase was found only when the nonfucosylated acceptors nLc4 and nLc6 were added, and none of the glycolipids with Lex structure (III3FucnLc4; V3FucnLc6; III3V3Fuc2nLc6) were sialylated; and (ii) the PC9 cell fucosyltransferase was active with both neutral and ganglioside neolacto (type 2 chain) acceptors. Transfer of fucose to VI3NeuAcnLc6 yielded mono- and difucosyl derivatives, whereas only a monofucosyl derivative was obtained when VI6NeuAcnLc6 was the acceptor. This is most probably due to different conformations at the terminus of the two acceptor gangliosides. The fucosyltransferase was incapable of transferring fucose to sialyl 2----3 lactotetraosylceramide (IV3NeuAcLc4).
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PMID:Biosynthesis of the sialyl-Lex determinant carried by type 2 chain glycosphingolipids (IV3NeuAcIII3FucnLc4, VI3NeuAcV3FucnLc6, and VI3NeuAcIII3V3Fuc2nLc6) in human lung carcinoma PC9 cells. 241 36

Human melanoma cells express high levels of GM3 and GD3 gangliosides whereas normal melanocytes have only low levels of GD3 but maintain their expression of GM3. In order to understand the basis for this difference, the levels of the sialyltransferase that converts GM3 to GD3 (CMP-N-acetylneuraminic acid:GM3 sialyltransferase or GD3 synthase, EC 2.4.99.8) were analyzed in melanoma and other cell lines. Enzyme levels were determined in vitro using membrane preparations and measuring the addition of [14C]-N-acetylneuraminic acid from CMP-[14C]-N-acetylneuraminic acid to GM3 in the presence of Triton CF-54. Sialyltransferase levels in 44 human cancer cell lines (including melanoma, neuroblastoma, astrocytoma, various carcinomas, and leukemias) and cultures of normal melanocytes and kidney epithelial cells were compared, and the products were identified by thin layer chromatography and fluorography. Melanoma cell lines exhibited the highest levels of incorporation and GD3 was found to be the major product. GM3 was also formed, apparently from endogenous lactosylceramide. Very low levels of GD3 synthase were found in normal melanocytes. Neuroblastoma and some astrocytoma cell lines also had significant levels of GD3 synthase. Some other cell lines incorporated high levels of radioactivity but the products did not correspond to GD3 and the major product was usually GM3. In general the levels of GD3 synthase correlated with the expression of GD3 in the various cell types. These results point to higher levels of GD3 synthase being directly responsible for the enhanced expression of GD3 in melanoma.
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PMID:Sialyltransferase levels and ganglioside expression in melanoma and other cultured human cancer cells. 280 71

Peptide maps of Form A and Form B of porcine submaxillary gland beta Gal alpha 2----3 sialyltransferase were essentially identical, consistent with the view that the two forms are not different enzyme species but that one, the B form (Mr = 44,000) is derived from the A form (Mr = 49,000). Analysis of the sialyltransferase activity in subcellular fractions from homogenates of porcine submaxillary glands reveals that 85% of the total activity of the transferase is bound to membranes, mostly in the Golgi apparatus, and that the remainder is soluble. The relative amounts of the membrane-bound and soluble forms as well as their response to detergents suggests that they are the cellular counterparts to the A and B forms of the transferase. The activity of Form A and the membrane-bound enzyme is stimulated to similar extents by various detergents. Triton-type detergents are more effective than Brij-type. Lysophosphatidylcholine is a potent stimulator of the activity of Form A but lysophosphatidylethanolamine is without effect and lysophosphatidylserine and lysophosphatidylglycerol are inhibitory. C16-18 acyl derivatives of lysophosphatidylcholine stimulate the activity more extensively than the C14 acyl derivative, and the C12 acyl derivative is without effect. In contrast, Form B is fully active in the absence of all detergents tested although it is inactivated just as Form A by lysophosphatidylglycerol and octylglucoside. Kinetic analysis of Forms A and B reveal that detergents stimulate the activity of Form A by lowering the KD and KM of CMP-NeuAc and increasing the Vmax of the reaction. Form B in contrast, which is fully active in the absence of detergents, has kinetic parameters like those of Form A in the presence of detergent. Taken together, these results suggest that Form A of the sialyltransferase, but not Form B, contains a lipid-binding domain, and that binding of detergents or lipids to the domain modulates the activity of the enzyme.
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PMID:Regulation of beta-D-galactoside alpha 2----3 sialyltransferase activity. The effects of detergents and lysophosphatidates. 385 Sep

A sialyltransferase which catalyzes the in vitro biosynthesis of N-acetylneuraminosyllacto-N-neohexaosylceramide from lacto-N-neohexaosylceramide and CMP-NeuAc has been examined in embryonic chicken breast muscle. The maximum enzyme activity was observed in 11-12-day-old embryos. The enzyme has optimum activity at pH 6.8 in the presence of Triton CF-54 and Mg2+. The apparent Km values for lacto-N-neohexaosylceramide and CMP-NeuAc were 0.9 and 0.67 mM, respectively. The enzymic product was characterized by TLC, neuraminidase hydrolysis and permethylation analysis. The structure was identical to authentic N-acetylneuraminosyllacto-N-neohexaosylceramide from chicken muscle. In addition, a disialo derivative has been detected that constitutes 15% of the total radioactivity incorporated. The two sialic acids connected by sialosyl-sialosyl linkage were attached to the terminal galactose residue. To our knowledge, this is the first report of biosynthesis of this disialo compound.
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PMID:Sialylation of lacto-N-neohexaosylceramide by sialyltransferase from embryonic chicken muscle. 395 72


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