Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.99.6 (sialyltransferase)
 1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Incubation of rat jejunal slices in Krebs-Ringer bicarbonate buffer (KRB) required the presence of heat-inactivated horse serum (HHS) in order to show time-dependent release of sialyltransferase into the medium. Sialyltransferase activity could not be detected in the medium when KRB alone or KRB supplemented with either albumin or glycerol was used in the incubations. The viability of the jejunal slices for up to 4 h of incubation was determined by studying the incorporation of glucosamine and leucine into acid-insoluble proteins. Supplementation of KRB with HHS had no beneficial effect on the rate of incorporation of leucine and glucosamine into proteins. KRB medium obtained after different periods of incubation contained higher trypsin-like activity than KRB medium containing HHS. Various antiproteases present as supplements to KRB resulted in the release of sialyltransferase activity from the jejunal slices. Among these antiproteases, alpha 1-proteinase inhibitor (alpha 1-PI) was the most effective. Also, HHS added to KRB immediately following incubation resulted in partial restoration of sialyltransferase activity in the medium, suggesting the presence of anti-proteolytic factors in HHS. The addition of increasing concentrations of heparin to incubations containing HHS caused a decrease in the medium sialyltransferase activity. The heparin-binding fraction (HBF) from HHS, when added to incubations, was able to protect the sialyltransferase released into medium. However, HHS depleted of its heparin-binding fraction by heparin-agarose affinity chromatography was unable to protect the sialyltransferase. HBF was separated into high- and low-molecular-mass fractions (fractions A and B respectively) by gel-filtration chromatography. The capacity to protect the released sialyltransferase was contained in fraction B. Fraction A contained multiple bands on SDS/PAGE and did not protect the enzyme. Fraction B contained a major protein band on the gel which corresponded to the migration of a similar band in human alpha 1-PI. HBF as well as fraction B isolated from HHS showed anti-trypsin-like activity. The results presented indicate that HHS contains a heparin-binding protein(s) similar to human alpha 1-PI which plays a role in the protection of sialyltransferase released from jejunal slices.
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PMID:Heparin-binding serum protein(s) is required for the protection of sialyltransferase released during the incubation of rat jejunal slices. 176 33

We are interested in determining whether carbohydrates are important regulatory determinants in the intracellular transport and secretion of glycoproteins. In the present study, we have used swainsonine, an indolizidine alkaloid, to modify the structure of N-glycosidically linked complex oligosaccharides. By inhibiting Golgi mannosidase II, swainsonine prevents the trimming of GlcNAc(Man)5(GlcNAc)2 to GlcNAc-(Man)3(GlcNAc)2, resulting in the formation of hybrid-type oligosaccharides. We find, from pulse-chase experiments using [35S]methionine and immunoprecipitation of individual proteins from culture media, that swainsonine treatment (1 microgram/ml) accelerated the secretion of glycoproteins (transferrin, ceruloplasmin, alpha 2-macroglobulin, and alpha 1-antitrypsin) by decreasing the lag period by 10-15 min relative to untreated cultures. The enhanced secretion was specific for glycoproteins since the secretion of albumin, a nonglycoprotein, was unaffected. When alpha 1-antitrypsin was immunoprecipitated from the cell lysates, sodium dodecyl sulfate-polyacrylamide gel electrophoresis fluorographic analysis demonstrated that the conversion of the high-mannose precursor to the hybrid form in swainsonine-treated cells occurred more rapidly (by about 10 min) than the conversion to the complex form in control cells. Since both the hybrid and complex forms of alpha 1-antitrypsin are terminally sialylated by sialyltransferase in the trans-Golgi, these results suggest that swainsonine-modified glycoproteins traverse the Golgi more rapidly than their normal counterparts. Therefore, accelerated transport within this organelle may account for the decreased lag period of glycoprotein secretion in the swainsonine-treated cultures.
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PMID:Swainsonine treatment accelerates intracellular transport and secretion of glycoproteins in human hepatoma cells. 257 69

Liver slices from control and 24hr inflamed rats were incubated for up to 20hr with 5mM 1-deoxynojirimycin (DN), an inhibitor of the processing glucosidases. The amounts of albumin and alpha 1-acid glycoprotein (AGP) and the activities of sialyltransferase were determined in liver and medium. The presence of DN significantly inhibited the release of AGP and sialyltransferase. The inhibitory effect of DN was most pronounced with slices from inflamed rats. Secretion of albumin was not inhibited. Incorporation studies with labelled leucine and mannose showed that the inhibitor did not significantly affect protein synthesis, but it did inhibit mannose incorporation into AGP and sialyltransferase. The results show that DN inhibits the secretion of acute phase AGP and sialyltransferase in liver slices and further suggests that sialyltransferase is a glycoprotein.
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PMID:Studies on the effect of 1-deoxynojirimycin on the release of albumin, sialyltransferase and alpha 1 acid glycoprotein from liver slices from normal and inflamed rats. 297 May 69

We have recently demonstrated the presence of sialyltransferase and sialic acid in a trans-tubular network (TTN) continuous with trans Golgi apparatus cisternae of rat liver hepatocytes. Based on these findings, we concluded that this structure, which also exhibited thiamine pyrophosphatase and acid phosphatase activity, is an integral part of the Golgi apparatus and functions in sialylation. In the present study, by comparing the distribution of a major hepatocyte secretory product with that of sialyltransferase, we sought to determine whether the TTN is also part of the secretory pathway. Examination of adjacent serial thin sections labeled for albumin showed its presence throughout the TTN and simultaneously provided new details about the structural complexity of the TTN. Double-immunolabeling with protein A-gold allowed the direct demonstration of albumin throughout the sialyltransferase containing TTN. Additional double staining protocols (combination of preembedding enzyme cytochemistry with postembedding immunolabeling) revealed the presence of albumin in both the thiamine pyrophosphatase and acid phosphatase positive regions of the TTN. These data show that albumin, a nonglycosylated secretory protein, reaches the TTN where terminal glycosylation of glycoproteins occurs. Therefore, it appears that the TTN of rat hepatocytes which functions in terminal glycosylation is also part of the constitutive secretory pathway.
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PMID:The trans-tubular network of the hepatocyte Golgi apparatus is part of the secretory pathway. 302 5

Liver slices from control and inflamed rats were incubated in McCoy's medium and incorporation of [3H]leucine into liver and medium proteins and into albumin and alpha 1-acid glycoprotein was monitored over 48 hr. The release of the new acute phase reactant, sialyltransferase was also monitored in this system. Earlier observations in which liver slices were incubated for 6 hr showed that increased leucine incorporation into liver and medium proteins and alpha 1-acid glycoprotein, coupled with decreased incorporation into albumin, correlated with the acute phase response of these proteins. Increased incorporation of leucine into these proteins was found following 48 hr incubation in McCoy's medium showing that slices were able to express the changes characteristic of the acute phase response over this longer time period of incubation. Sialyltransferase was released into medium in a linear fashion up to 15 hr and continued to increase for 30 hr in this system; there was a substantial increase in release of enzyme activity from slices from inflamed rats when compared to controls. Monokine-conditioned medium prepared from peritoneal exudate cells isolated from rats at various times after lipopolysaccharide administration was used to induce the acute phase response by intraperitoneal injection. Slices were prepared from these rats and sialyltransferase release from slices was monitored. Monokines prepared from peritoneal exudate cells isolated from rats at about 30 hr were most effective in stimulating sialyltransferase release from liver slices.
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PMID:Studies on the effect of inflammation on the acute phase response using rat liver slices. 310 62

The role of monocyte derived factors in the acute phase response to inflammation is discussed. The kinetics of response of alpha 1-acid glycoprotein, sialyltransferase and albumin to a rat monokine preparation is described. There was an increase in synthesis of alpha 1-acid glycoprotein and sialyltransferase and a decrease in albumin synthesis following administration. However, the kinetics of response of sialyltransferase to the monokine was much slower than was found for the other two proteins. The possibility that sialyltransferase responds to a different monokine compared to the other acute phase proteins is discussed.
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PMID:The acute phase response to inflammation: the role of monokines in changes in liver glycoproteins and enzymes of glycoprotein metabolism. 311 78

Cystic fibrosis and normal plasma proteins were compared by the method of high resolution two-dimensional electrophoresis in polyacrylamide gels. For the first dimension, samples were treated with urea and dithiothreitol and then subjected to isoelectric focusing in pH gradients of 3.5-10.0 or 5.0-8.0. The second dimension involved sodium dodecyl sulfate electrophoresis into gels of 10-20% polyacrylamide gradients. In one "blind" experiment, an attempt to segregate 12 plasma samples into six cystic fibrosis and six normals based on the polypeptide patterns was unsuccessful. Experiments using known cystic fibrotic and normal plasma samples (three further samples of each), depleted of albumin prior to electrophoresis, also failed to confirm the presence of cystic fibrosis related proteins or peptides. We have not been able to substantiate, by electrophoretic means, changes of sialic acid content of any plasma glycoprotein which might be expected to occur, for example, as a result of the postulated altered sialyltransferase activity in cystic fibrosis liver.
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PMID:Comparison of the polypeptide composition of cystic fibrosis plasma with normal plasma by high resolution electrophoresis. 705 6

Higher level of terminal deoxynucleotidyl transferase (TdT) and peanut agglutinin (PNA)-positive cells were found in those fractions of albumin gradient separated rat thymocytes that had a higher level of glucocorticoid (GC) receptors and a lower level of sialyltransferase (S-T) activity. Incubation of thymocytes in these fractions with dexamethasone inhibited RNA synthesis significantly. Incubation of these thymocytes with tetradecanoylphorbol-acetate (TPA) reduced TdT activity, while increasing S-T activity. The higher level of GC receptors may be responsible for GC sensitivity of TdT-positive thymocytes. In addition, sialyltransferase may be a biochemical marker for thymocyte differentiation.
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PMID:Terminal deoxynucleotidyl transferase and glucocorticoid receptors in rat thymocytes. 811 29

1. Sialyltransferase is a liver Golgi membrane-bound enzyme that is released from the liver under conditions of experimental inflammation. Previous work showed that the action of a cathepsin D-like proteinase was responsible for release of the enzyme from isolated Golgi membranes. This study shows that the same enzyme is responsible for release of sialyltransferase in whole-cell systems. 2. Gal beta 1-4GlcNAc alpha 2-6sialyltransferase (EC 2.4.99.1) was secreted from slices of rat and mouse liver into the incubation medium with larger amounts of activity being secreted from slices of liver from animals suffering from experimental inflammation. 3. The presence in the incubation medium of the cathepsin D proteinase inhibitor, pepstatin A, at 10(-4) M was sufficient to inhibit the release of sialyltransferase into the medium by about 60% after a 6 hr incubation. 4. The release of albumin and alpha 1 acid glycoprotein from rat liver slices, was not affected by the presence of pepstatin A, indicating that the proteinase inhibitor did not affect the synthesis and secretion of typical secretable proteins by the liver. 5. Intraperitoneal injections of pepstatin A into mice prior to preparation of liver slices also resulted in a significant reduction of the secretion of sialyltransferase into the incubation medium. 6. The results from these studies support the idea that a cathepsin D-like proteinase is responsible for the release of sialyltransferase into the extracellular space in whole cells in the rat and the mouse.
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PMID:Evidence for the role of a cathepsin D-like activity in the release of Gal beta 1-4GlcNAc alpha 2-6sialyltransferase from rat and mouse liver in whole-cell systems. 844 97

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


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