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)

A sialyltransferase involved in the biosynthesis in vitro of LD1c (NeuAc alpha 2-8NeuGc alpha 2-3Gal beta 1-4Glc-NAc beta 1-3Gal beta 1-4Glc-Cer) has been characterized from 9 to 11-day-old embryonic chicken brains. The CMP-[14C]NeuAc:LM1(alpha 2-8)sialyltransferase (SAT-2) sedimented (75%) at the junction of 0.75 and 1.2 M on a discontinuous sucrose density gradient when still membrane bound. In addition to the biosynthesis of LD1c, the detergent-solubilized (0.4% Nonidet P-40) preparation also catalyzes the transfer of sialic acid to O-8 of sialic acid in GM3 to form GD3 (NeuAc alpha 2-8NeuAc alpha 2 - 3Gal beta 1 - 4Glc - Cer). Substrate inhibition studies indicated that these two reactions are probably catalyzed by the same enzyme, SAT-2. The kinetic parameters of SAT-2 activity were determined. The Km values were 70 and 63 microM with CMP-[14C]NeuAc and LM1, respectively, when the detergent-solubilized supernatant fraction was used as enzyme source. The (alpha 2-8)-linkage between the terminal and penultimate sialic acids was determined using nonradioactive CMP-NeuAc and [Ac-14C]LM1 as substrates (Higashi, H., and Basu, S. (1982) Anal. Biochem. 120, 159-164) for the enzyme, followed by identification of the permethylated [14C]sialic acid of the product by radioautography. At 0.5 mM N-ethylmaleimide, the SAT-2 activity was inhibited 50% whereas SAT-1 and SAT-3 activities (Basu, M., Basu, S., Stoffyn, A., and Stoffyn, P. (1982) J. Biol. Chem. 257, 12765-12769) remained uninhibited.
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PMID:Biosynthesis in vitro of disialosylneolactotetraosylceramide by a solubilized sialyltransferase from embryonic chicken brain. 383 72

Studies on developmental changes of ganglioside synthesis and compositions were carried out using rat bone marrow cells, spleen and thymus. Ganglioside synthesis was studied by assaying sialyltransferase for GM3 synthesis and GM1b synthesis. In bone marrow cells, peaks of both enzyme activities occurred coincidentally in 2- to 5-week-old rats. In spleen, the highest activities of these enzymes were observed in one-week-old rats. GM1b synthesis in the thymus was almost constant after birth, but GM3 synthesis could not be detected at any age examined. Developmental changes of gangliosides in these tissues were analyzed by thin layer chromatography. Gangliosides corresponding to GM1b and GM3 were recognized in each tissue. The ganglioside content of the bone marrow cells increased in 2- to 5-week-old rats. Ganglioside corresponding to GM1b was isolated from the bone marrow cells, and its structure was confirmed to be the same as that of GM1b by sequential hydrolysis of the ganglioside with glycosidases. GM3 was a predominant ganglioside in newborn rat spleen. Ganglioside content in the spleen increased during 2-5 weeks after birth and became constant after 9 weeks. In the thymus, more than 10 different gangliosides were discriminated, but significant changes of ganglioside pattern with the progress of development could not be observed. The developmental change of the ganglioside composition coincided well with the change of sialyltransferase activities.
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PMID:Developmental changes of ganglioside compositions and biosyntheses in rat bone marrow cells, spleen and thymus. 664 28

Golgi vesicles were isolated and purified from rat liver, in which the specific activities of glycosyltransferases (e.g. GM3: CMP-NeuAc sialyltransferase, GD3-synthase; GM3: UDP-GalNAc galactosaminyltransferase, GM2-synthase) were 50-60 times enriched relative to microsomes or total homogenate. Synthesis of gangliosides GM2 and GM1 in such Golgi vesicles is, in the absence of any detergents, stimulated 6- and 20-fold, respectively, by phosphatidylglycerol. Other phospholipids like dolichyl phosphate, phosphatidylethanolamine and phosphatidylserine are also significantly stimulatory. Tunicamycin inhibits the synthesis of gangliosides GM2 and GM1 in isolated Golgi vesicles, but only in the absence of detergents. The dependence on phosphatidylglycerol and the degree of inhibition by tunicamycin of the synthetic activities are strictly dependent on the intactness of the Golgi vesicles: both phenomena become increasingly less evident when the vesicles are pelleted, and frozen and thawed several times, and completely disappear when the vesicles are solubilized by the detergents or disrupted by ultrasonication. Furthermore, tunicamycin inhibition is reversible by increased concentration of phosphatidylglycerol. In pronase-treated Golgi vesicles, which retain full enzyme activity, both phospholipid-dependence and tunicamycin inhibition of the synthetic activity disappear completely. When freshly prepared Golgi vesicles are incubated with 125 microM UDP [3H]Gal for 10 min at 30 degrees C, the nucleotide sugar is found to be transported into the vesicles at the rate of about 85 pmoles/mg protein/min, 92% of radiolabel remaining firmly bound with membrane. Tunicamycin inhibits this transport in a concentration-dependent manner. The results show that, while the mechanism of phosphatidylglycerol induced stimulation of the synthetic activity remains unclear, tunicamycin inhibits ganglioside biosynthesis by blocking the transport of the nucleotide sugar across Golgi vesicles and not inhibiting the transferase enzyme directly.
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PMID:Ganglioside biosynthesis in rat liver golgi apparatus: stimulation by phosphatidylglycerol and inhibition by tunicamycin. 674 31

We isolated the Golgi-rich fraction from rat ascites hepatoma AH-130 cells and rat liver, and compared some properties of glycosyltransferases using various acceptors. The specific activity of sialyltransferase in the hepatoma Golgi fractions was reduced to 19--41% depending upon the acceptor used (asialo-orosomucoid, asialo-fetuin or asialo-mucin), as compared to that of the normal liver Golgi fraction. However, no significant difference between the enzymes from the two sources was observed in pH optimum, requirements for the enzyme activity, and Km values for the donor substrate (CMP-sialic acid) and various acceptors used. The specific activity and other kinetic parameters of hepatoma galactosyltransferase were not significantly different from those of the liver enzyme, when assayed with N-acetylglucosamine, asialo-agalacto-fetuin and asialomucin as acceptors. Glycosyltransferases in the hepatoma and liver Golgi fractions were then assayed with plasma membranes from both sources as exogenous acceptor. Hepatoma sialyltransferase activity was much lower (1/2 to 1/4) than that of the normal liver. Galactosyltransferase activity, however, was found to be slightly higher in the hepatoma Golgi fraction than in the normal liver. Acceptor plasma membranes which were thus glycosylated in vitro by each Golgi enzyme were separated into protein and lipid fractions, and the latter fraction was further analyzed by thin layer chromatography. The results suggest that the hepatoma Golgi had much lower levels of glycoprotein : sialyltransferase and asialo-GM1 : sialyltransferase, but had an increased activity of asialo-GM3 : sialyltransferase. It is also suggested that the hepatoma Golgi had a high activity for the formation of di- and tri-glycosylceramides, for which the liver Golgi showed negligible activity.
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PMID:Characterization of glycosyltransferases in the Golgi complex from rat ascites hepatoma AH-130 cells: a comparison with those from normal liver. 681 67

The postnatal development of mammalian skeletal muscle is characterized by changes in the properties of several key membrane glycoprotein enzymes and receptors. In the present study, CMP-sialic acid: fetuin sialyltransferase and CMP-sialic acid: lactosylceramide sialyltransferase activity was characterized in sarcolemma and sarcoplasmic reticulum membranes isolated from neonatal (0-1 week) and adult (8 week) rabbit skeletal muscle. CMP-sialic acid: fetuin sialyltransferase decreased by a factor of 10 in sarcolemma and 6 in sarcoplasmic reticulum during development, whereas CMP-sialic acid: lactosylceramide sialyltransferase activity decreased by a factor of 6 in sarcolemma and 18 in sarcoplasmic reticulum. The Km for CMP-sialic acid using the lipid acceptor declined during the development of sarcoplasmic reticulum (neonate vs. adult: 538 vs. 33 microM), but not in sarcolemma. The carbohydrate composition of sarcolemma was changed only with respect to total sialic acid content (neonate vs. adult: 67 vs. 44 nmol/mg). Similar analysis of sarcoplasmic reticulum carbohydrates showed decreases in total sialic acid, lipid-bound sialic acid, hexosamines and hexoses. The major ganglioside was GM3 for both types of membrane. No qualitative changes were observed in ganglioside composition comparing neonatal and adult membranes.
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PMID:Studies on glycoconjugate metabolism in developing skeletal muscle membranes. 682 28

Golgi vesicles were isolated and purified from rat liver, in which the specific activities of glycosyltransferases (e.g. GM3:CMP-NeuAc sialyltransferase, GD3 synthase; GM3:UDP-GalNAc galactosaminyltransferase, GM2 synthase) were 50-60-times enriched relative to microsomes or total homogenate. Synthesis of gangliosides GM2 and GM1 in such Golgi vesicles is, in the absence of any detergents, stimulated 6-fold and 20-fold respectively by phosphatidylglycerol. Other phospholipids like phosphatidylethanolamine and phosphatidylserine are also significantly stimulatory. With 50 micrograms Golgi protein and 1 nmol UDP-GalNAc, optimal stimulation of GM2 synthase was obtained with 20 micrograms of phosphatidylglycerol and 7.5 nmol of the lipid acceptor GM3. Under the same experimental conditions this stimulation exceeds (by about 40%) that obtained with optimal amount (200 micrograms) of the detergent octylglucoside. Phosphatidylglycerol, on the other hand, has virtually no stimulatory activity on the synthesis of ganglioside GD3 either in the presence of Mg2+ or Mn2+, indicating that facilitation by phospholipid of GM3 transport into Golgi vesicles was not the basis of stimulation of GM2 synthesis. Tunicamycin inhibits the synthesis of gangliosides GM2 and GM1 in isolated Golgi vesicles, but only in the absence of detergents. In the presence of phosphatidylglycerol, GM2 synthesis, for example, was inhibited by 60% by 2 micrograms tunicamycin and more than 85% by 10 micrograms tunicamycin, per 50 micrograms Golgi membrane protein. The inhibition was stronger on GM1 synthesis: 85% with 2.5 micrograms of the antibiotic. The dependence on phosphatidylglycerol and the degree of inhibition by tunicamycin of the synthetic activities are strictly dependent on the intactness of the Golgi vesicles: both phenomena become increasingly less evident when the vesicles are pelleted, and frozen and thawed several times, and completely disappear when the vesicles are solubilized by detergents or disrupted by ultrasonication. Furthermore, tunicamycin inhibition is reversible by increased concentration of phosphatidylglycerol. All these results indicate that phosphatidylglycerol does not stimulate, and tunicamycin does not inhibit, the transferases themselves; rather, the two opposing effects might relate to carrier-mediated transport, e.g. of nucleotide sugars, across Golgi vesicles.
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PMID:Ganglioside biosynthesis in Golgi apparatus of rat liver. Stimulation by phosphatidylglycerol and inhibition by tunicamycin. 686 62

The correlation between levels of sialic acid and sialic acid-containing glycolipids (gangliosides) in tumors and serum with the growth characteristics of the tumors was investigated in transplantable hepatomas and squamous cell carcinomas initiated with the carcinogen N-2-fluorenylacetamide and propagated in vivo and in tissue culture. Tumor lines varied in histologic classification, growth rate, and ability to form pulmonary metastases. There was neither a correlation between growth rate and histologic classification nor between either of these two parameters and the ability to metastasize. Total and ganglioside sialic acid levels were elevated in carcinogen-treated liver and in transplantable hepatomas when contrasted with normal liver. Levels of sialic acid showed a weak correlation with the growth rate of hepatomas. Gangliosides from nonmetastatic hepatoma lines exhibited less N-acetylneuraminic acid--galactose--glucose-N--acylsphingosine (GM3) and an increased ratio of total monosialogangliosides to disialogangliosides than did metastatic lines. Ganglioside patterns of metastatic hepatoma lines more closely resembled the ganglioside patterns of normal liver than did those of the nonmetastatic lines. Concomitant elevations of total and ganglioside sialic acid levels were observed in sera of animals bearing subcutaneous implants. Serum levels of total sialic acid did correlate with total sialic acid levels found in the tumor tissues. The levels of serum sialic acid were not correlated directly with levels of serum sialyltransferase activity. Elevations of both tissue and serum ganglioside sialic acid were consistent features of liver tumorigenesis in the rat after N-2-fluorenylacetamide administration. They appeared, furthermore, to be early events not directly related to tumor cell differentiation or metastasis.
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PMID:Characteristics of transplantable tumors induced in the rat by N-2-fluorenylacetamide: elevations in tissue and serum sialic acid. 692 77

Total labeled glycolipids from thymocytes of leukemic AKR/J mouse thymus incubated for 24 h in the presence of the precursors [3H] galactose or [14C] glucosamine were found to exceed those from non-leukemic thymocytes. The amount of labeled compounds that co-migrated with monosialogangliosides (GM3 and GM2) and disialogangliosides (GD1a and GD1b) was higher, whereas incorporation into monosialoganglioside (GM1) and trisialoganglioside (GT1) was lower in leukemic than in non-leukemic thymocytes. Consistent with this altered pattern of ganglioside distribution was the finding of a higher activity of two of the sialyltransferase activities in homogenates of leukemic thymus as compared to normal thymus. About 2-fold higher activities of the enzymes CMP-AcNeu: lactosylceramide sialyltransferase and CMP-AcNeu: GM1 sialyltransferase were observed in leukemic thymus homogenate compared to homogenates of non-leukemic cells. The substrate affinity of sialyltransferase with GM1 as acceptor from the leukemic thymus was similar to that of the enzyme from normal thymus. Thus, our studies reveal an enzymatic basis for the enhanced rate of synthesis and altered ganglioside profile observed in malignant thymocytes, and are consistent with the general view on the pattern of acidic glycolipids in tumorigenesis.
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PMID:Glycolipid sialyltransferases in normal and neoplastic murine thymocytes. 731 48

Sodium butyrate and dimethylsulfoxide (DMSO) have marked effects on the growth, morphology, and biochemistry of two human colonic adenocarcinoma cell lines in culture. Doubling times were increased between 18% and 660% while cell viability was unaffected. Both cell lines formed colonies in soft agar in the absence of butyrate of DMSO, but no colonies were observed in the presence of these agents. However, no differences in in vivo tumorigenicities, when cells were implanted in athymic mice, were seen following treatment. Gross morphological alterations including cell enlargement, process formation, and cellular flattening occurred during culture in butyrate or DMSO. Acrylamide gel electrophoresis in sodium dodecyl sulfate revealed no change in membrane protein constituents, but autoradiographic analysis of membrane glycoproteins demonstrated differences between treated and untreated cells. Ganglioside compositions were altered, and a sialyltransferase required for the synthesis of GM3 ganglioside was elevated by butyrate. Although cytoplasmic aminooligopeptidase remained unaffected by butyrate or DMSO, brush border-associated activity was enhanced by butyrate. Alkaline phosphatase also rose dramiatically during culture in butyrate but was not enhanced by DMSO.
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PMID:Effects of sodium butyrate and dimethylsulfoxide on biochemical properties of human colon cancer cells. 735 11

CMP-NAcNeu:GM3 ganglioside sialyltransferase (GD3 synthase) was characterized with respect to regulation of activity by nucleotides and compared in this regard with other sialyltransferases of ganglioside biosynthesis. Nucleotides preferentially inhibited the activity of GD3 synthase. Di- and trinucleotides inhibited most strongly and cytidine nucleotides were the most inhibitory class. The mode of inhibition by CMP (competitive or noncompetitive) varied with storage conditions of Golgi apparatus membranes; CMP inhibition was decreased during a series of consecutive freeze-thawings of membranes. Also, GD3 synthase inhibition by CDP was only partially relieved by excess Mg2+. With lactosylceramide as the in vitro precursor, synthesis of GM3 was always less inhibited by cytidine nucleotides than was that of GD3 and GT3. An 8-fold reduction in the ratio GD3/GM3 in the reaction products was obtained at 1.5 mM CTP. Separate incubations for the sialylation of GM3 or GM1 showed cytidine nucleotides increased synthesis of GD1a relative to GD3 by 3.5-fold.
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PMID:Ganglioside biosynthesis in rat liver: alteration of sialyltransferase activities by nucleotides. 740 17


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