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:2.4.99.6 (sialyltransferase)
1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The total, glycoprotein-bound and glycolipid-bound sialic acid concentration, ad the activities of ecto-sialyltransferase and neuraminidase were determined in synaptosomes from preweanling ethanol-treated and control rats. The period of treatment corresponded to that of maximal synaptogenesis and peak synthesis of sialoglycocompounds (days 27-37 postconception). The average of the peak blood ethanol concentration was 271 mg/100 ml. In the ethanol-treated animals the sialic acid concentration was significantly reduced (approximately 20%) with an equally distributed decrease of glycoprotein- and glycolipid-bound sialic acid. The activity of ecto-sialyltransferase with asialofetuin as exogeneous acceptor was significantly diminished (about 30%) in the ethanol-treated pups. Neuraminidase showed an unchanged activity after correction for the reduction of endogeneous sialic acid substrate concentration. The total protein and lipid concentrations of the synaptosomal preparations did not differ between the groups. These results suggest that ethanol treatment during on of the vulnerable periods of brain development causes an inhibition of the incorporation of sialic acid into synaptosomal membrane-bound sialoglycocompounds. Such an effect of ethanol exposure might disturb intercellular interactions and the functional performance of the membrane during development, and could be of importance in the pathogenesis of the central nervous system manifestations of the fetal alcohol syndrome.
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PMID:Effect of ethanol on synaptosomal sialic acid metabolism in the developing rat brain. 685 42

Rat liver Golgi was found to contain a sialyltransferase activity which would convert lacto-N-tetraose (Gal beta 1 goes to 3GlcNAc beta 1 goes to 3Gal beta 1 goes to 4Glc) to LS-tetrasaccharide a (NeuAc alpha 2 goes to 3Gal beta 1 goes to 3GlcNAc beta 1 goes to 3Gal beta 1 goes to 4Glc). The enzyme has been partially purified by affinity chromatography on CDP-hexanolamine agarose. Of the glycoprotein substrates examined, it utilizes the Gal beta 1 goes to 3GlcNAc sequence found on the asparagine-linked oligosaccharides of prothrombin as its preferred acceptor substrate, and thus has been tentatively designated a Gal beta 1 goes to 3GlcNAc alpha 2 goes to 3 sialyltransferase. The partially purified enzyme has an acceptor specificity distinct from other purified mammalian sialyltransferases which synthesize the NeuAc alpha 2 goes to 3Gal beta 1 goes to 3 GalNAc and NeuAc alpha 2 goes to 6 GalNAc sequences common to oligosaccharides O-linked to threonine or serine and the NeuAc alpha 2 goes to 6Gal beta 1 goes to 4GlcNAc sequence found on oligosaccharides N-linked to asparagine.
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PMID:Identification of a Gal beta 1 goes to 3GlcNAc alpha 2 goes to 3 sialyltransferase in rat liver. 706 22

Asialomucin-sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity was solubilized from mouse liver microsomes by sonication. The catalytic activity was markedly inhibited by a series of lysophosphatidylcholines, particularly 1-palmitoyl-sn-glycero-3-phosphorylcholine. This lysophospholipid did not alter optimal conditions for enzyme activity. In contrast, it was found that affinities for binding of Mn2+, desialylated mucin and CMP-sialic acid were decreased by adding the lipid. A reasonable interpretation of these data is that the presence of phospholipid modifies the enzyme conformation.
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PMID:Effects of 1-palmitoyl-sn-glycero-3-phosphorylcholine on the properties of a solubilized sialyltransferase activity from mouse liver. 712 92

A simple procedure has been developed for purifying solubilized human liver glycoprotein sialyltransferase (EC 2.4.99.1) 16000-fold in 4-5% yield. The procedure involves two centrifugation steps, affinity chromatography of the ultrasupernatant fluid on cytidine diphosphate-hexanolamine-agarose followed by gel filtration on Sephadex G-150. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that the purified sialyltransferase preparation contains approximately equivalent amounts of three protein bands (with apparent molecular weights of 61000, 63000 and 70000) and is highly purified if not homogeneous.
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PMID:Purification of human liver glycoprotein sialyltransferase by affinity chromatography. 713 Jun 20

It has been known that cervical mucus can enhance or impede the passage of spermatozoa through the cervical canal. Cervical mucus consists of 2 major fractions, an insoluble gel or mucin, and an aqueous phase containing the soluble components (lipids; fatty acids; prostaglandins; trace metals; proteins; enzyme inhibitors, and immunoglobulins). Mucins are glycoproteins which are characterized by a proportion of more than 40% carbohydrates distributed along the peptide core. Ultrastructure studies of cervical mucin using transmission electron microscopy suggest either a filamentous or honeycomb-like structure. It has also been suggested that the structural integrity of cervical mucin is partly dependent on its sialic acid content, which is increased in midcycle mucin. This raises the issue concerning the type of mucus secreted by the cervical mucosa and whether the structural change of the mucin observed at midcycle is due to the transfer of sialic acid by sialyltransferase to the glycoprotein molecules by the mucin in the cervical canal. If the role of the cervical mucus in the capacitation of the spermatozoa and the mechanism of fertilization is established, it might explain some cases of infertility and cervical cancer, and may be useful in the development of alternative forms of contraception.
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PMID:Cervical mucus: its structure and possible biological functions. 718 80

Ovine submaxillary asialo-mucin was [14C]sialylated in vitro using a porcine liver cell-free preparation. The oligosaccharide chains were cleaved from the product glycoprotein by beta-elimination under reductive conditions, fractionated by gel filtration on Bio-Gel P-2 and characterized by thin-layer chromatography. The structure of the product chain was studied by periodate oxidation and analysis of the peeling products formed in the beta-elimination step. It appeared that [14C]-sialic acid had been introduced exclusively to the galactose residues of Gal beta(1 leads to 3)GalNAc disaccharide units occurring on the mucin as minor chains. No indication for a transfer to GalNAc residues on this glycoprotein was obtained. In agreement with this result sialyltransferase activities of porcine, rat, human and canine liver with Gal beta (1 leads to 3)GalNAc-protein acceptors were invariably much higher than those with ovine submaxillary asialo-mucin. When the asialo-mucin had been [14C]sialylated by an ovine submaxillary gland cell-free preparation analysis of the product oligosaccharide chain revealed the introduction of [14C]sialic acid to position C-6 on the GalNAc residues. The specificity of this transfer was reflected by the very high sialyltransferase activities of gland preparations with Gal beta (1 leads to 3)GalNAc-protein as well as GalNAc-protein acceptors. Mixed enzyme experiments indicated that the difference in liver and gland ovine submaxillary asialo-mucin sialyltransferase activities was not due to the presence of a specific inhibitor in the liver or an activator in the gland. It is concluded that porcine liver and likely liver of rat, man and dog contains a Gal beta (1 leads to 3)GalNAc-protein sialyltransferase, which is involved in the sialylation of O-glycosidically linked carbohydrate chains on serum glycoproteins. GalNAc-protein sialyltransferase activity, which richly occurs in ovine submaxillary gland, however, appears to be lacking from liver tissue.
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PMID:Specificity of sialyltransferase: sialylation of ovine submaxillary mucin in vitro. 721 66

Smooth membrane preparations of 13-day embryonic chicken livers, characterized by electron microscopy and marker enzyme analyses, have been found to contain sialyltransferase activity which displayed precise acceptor specificity. One sialyltransferase transferred N-acetyl-neuraminic acid (NANA) and gal beta 1 leads to 4glycNAc beta 1 leads R structures. Evidence based on competition studies suggests that a second enzyme is present transferring this sugar to a gal beta 1 leads to 3gal-NAc alpha 1 leads to R structure. The enzyme capable of adding NANA to gal beta 1 leads to 4glcNAc beta 1 leads to R structures has a pH optimum of 5.5, a temperature optimum of 30 degrees C, and half-saturating values of 17 muM for CMP-NANA and 180 muM for galactoside termini on desialyzed alpha 1-acid glycoprotein. It is activated about 10-fold by Triton X-100, has no exogenous divalent cation requirement, and is inhibited by CTP, CDP, and CMP. The enzyme requires carbohydrate structures underlying the gal beta 1 leads to 4glcNAc terminus for maximal catalytic activity; the necessity of such precise specificities of sialyltransferases is discussed in the light of recent structural evidence for the carbohydrate moieties of several glycoproteins.
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PMID:The specificity of sialyltransferase activity in smooth membrane fractions of embryonic chicken liver. 722 24

The activities of plasma and fibroblast cytidine 5'-monophosphate-sialic acid:glycoprotein sialyltransferases of patients with cystic fibrosis have been found to be within the range of activities of age- and sex-matched normal controls when asialofetuin served as the sialic acid acceptor. The use of desialylated preparations of purified human plasma alpha 2-macroglobulin, as an acceptor, demonstrated 35 to 52% reduction in the incorporation of sialic acid into the alpha 2-macroglobulin from patients with cystic fibrosis as compared to that of alpha 2-macroglobulin from normal controls. The reduced sialylation was dependent upon the source of the alpha 2-macroglobulin acceptor but independent of the source (cystic fibrosis or normal) of the sialyltransferase enzyme. Using radiolabeled precursors, the rates of the synthesis of N-acetylneuraminic acid from N-acetyl-D-mannosamine, the release of sialic acid from glycoproteins and the conversion of free sialic acid into CMP-sialic acid have been determined in cultured skin fibroblasts from patients with cystic fibrosis and found to be not significantly different from those of normal controls.
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PMID:The metabolism of sialic acid in cystic fibrosis. 724 84

Based on indirect evidence it has been suggested that the liquefaction of human seminal plasma involves fibrinolytic and proteolytic enzymes and that the coagulum is formed by proteins. In this preliminary investigation evidence is presented for the involvement of seminal plasma sialyltransferase in liquefaction which suggests that the coagulum may be composed of glycoproteins. It is proposed that the glycoproteins form a polymer by the chelation of divalent metal ions via the carboxylic acid moieties of the sialic acid groups of the glycoproteins. The glycoprotein polymer may then be dismantled by the reduction of the meal ions by the oxidation of L-ascorbic acid, possibly allowing enzymes to complete the liquefaction process. A total of 100 semen samples from 30 male subjects whose semen profiles were considered "normal" by an independent assessor, were examined for the following: (i) liquefaction time of the seminal plasma; (ii) seminal plasma sialyltransferase activity; (iii) spermatozoal motility, defined as directional or nondirectional; (iv) spermatozoal count, and (v) seminal plasma content of free L-ascorbic acid, dehydroascorbic acid and glutathione. Linear regression analysis showed a significant correlation between sialyltransferase activity and the liquefaction time for seminal plasma. Similarly, multilinear regression analysis of the data showed that as the seminal plasma levels of L-ascorbic acid, total dehydroascorbic acid and glutathione increase, there is a decrease in spermatozoal motility and a decrease in the liquefaction time of the seminal plasma. The possible metabolic relationship of seminal plasma L-ascorbic acid and glutathione is discussed and a metabolic pathway is suggested.
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PMID:Seminal plasma biochemistry. I. Preliminary report: a possible mechanism for the liquefaction of human seminal plasma and its relationship to spermatozoal motility. 724 44

Porcine liver microsomes are capable of transferring sialic acid from CMP-NeuAc to [14C]galactosylated ovine submaxillary asialo-mucin, porcine submaxillary asialo/afuco-mucin and ganglioside GM1. The specificity of the porcine liver sialyltransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) towards the first acceptor, [14C]Gal-GalNAc-protein, was investigated by means of methylation studies on the oligosaccharides changes cleft-off from the sialylated product glycoprotein by beta-elimination under reductive conditions. It appeared that sialic acid was transferred solely to position C-3 of galactose residues on Gal beta(1 leads to 3)GalNAc disaccharide units. Transfer to GalNAc residues was completely absent. Competition experiments and heat activation studies suggested that the same enzyme also converts ganglioside GM1 to ganglioside GD1a. Therefore, this porcine liver sialyltransferase can be designated as a Gal beta(1 leads to 3)GalNAc-R alpha(2 leads to 3) sialyltransferase.
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PMID:Specificity of porcine liver gal beta (1 leads to 3)galnac-r alpha(2 leads to 3) sialyltransferase sialylation of mucin-type acceptors and ganglioside GM1 in vitro. 728 98


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