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

A large family (14 children) with congenital goiter whose parents are first cousins was studied. Thyroid tissue was obtained, after 125I in vivo labeling, from one of the siblings (JBM). Gel filtration of thyroid proteins indicated that thyroglobulin (Tg) eluted as a single symmetrical peak in the same position as authentic 19S Tg. Gel electrophoresis in a 7.5% sodium dodecyl sulfate-polyacrylamide gel revealed a major band with the same mobility and immunoreactivity as normal 19S Tg. Hydrolysis of the patient's Tg indicated that most of the radioactivity was mono- and diiodotyrosines. The yield of T4 from JBM Tg (26 pmol/mg protein) was 5-fold less than normal thyroid tissue (140 pmol/mg protein) and approximately half of that in thyroid tissue from endemic goiter (51 pmol/mg). Total T3 released from JBM Tg was similar to the other two tissues. When the carbohydrate content of normal and patient Tg was analyzed, there was no differences in glucosamine, galactose or mannose content. However, unlike normal and endemic-goiter Tg, that had a mean sialic acid content of 7.3 and 5.6 micrograms/mg protein, respectively, the sialic acid concentration of the patients Tg was only 0.3 microgram/mg. Sialyltransferase activity was readily demonstrated in homogenate from normal thyroid or endemic goiter, but no sialyltransferase activity was detectable in a homogenate of JBM-thyroid tissue. We conclude that the finding of severely hyposialylated Tg is linked to a defect in iodotyrosine coupling seen in this patient with a possibly abnormal migration of Tg into the follicular lumen.
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PMID:Hyposialylated thyroglobulin in a patient with congenital goiter and hypothyroidism. 172 28

A differential distribution of sialyltransferase (ST) in different regions of intestine has been shown. Jejunum and ileum homogenates from rats showed almost exclusive presence of alpha-2-3 ST (to Gal in Gal beta-1-4GlcNAc and/or to Gal in Gal beta-1-3GalNAc). In contrast, colon homogenates showed the presence of both alpha-2-3 ST (as above) and alpha-2-6 ST. Incubation of intestinal slices in presence of heat-inactivated horse serum (HHS) showed a time- and temperature-dependent secretion of soluble ST into the medium. Both jejunum and ileum slices showed high rates of secretion of alpha-2-3 ST. Colon slices, though rich in alpha-2-6 ST, secreted only alpha-2-3 ST. Colchicine, an anti-mitotic drug, injected into rats caused about 10-fold increase of the serum ST level. Jejunum slices from colchicine-treated rats showed an increased secretion of alpha-2-6 ST, suggesting that intestine undergoes a change in the expression of normal secretion of alpha-2-3 ST to a secretion of alpha-2-6 ST. The secretion of ST from incubated intestinal slices was inhibited by heparin. Certain protein factors (anti-proteases) in HHS bind to heparin-sepharose column and these protein factors are responsible for causing the secretion of ST into the medium. It has also been found that a supernatant fraction of the colon homogenate activated ST. Gel chromatography on HPLC produced 3-4 protein fractions from the colon cytosol and one of this fraction bearing high molecular weight proteins produced the maximum activation of ST.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Regulation of sialyltransferase activity in intestinal segments of rats. 210 89

1. Subcellular fractions isolated from livers of 19-day-old chicken embryos were analyzed in order to assess whether liver mitochondria contained glycosylated proteins or had mannosyl- or sialyl-transferases that could transfer sugars to mitochondrial macromolecules. 2. Proteins in liver mitochondrial membranes and matrix fractions were screened for their affinities for concanavalin A (Con A). 3. After separation by gel electrophoresis under denaturing conditions, a significant number of the proteins bound [125I]Con A, and the binding of the lectin was substantially inhibited by alpha-methyl-D-mannoside. 4. In addition, radio-iodinated matrix proteins were screened for lectin-binding properties by chromatography on Con A covalently linked to agarose. 5. A number of proteins, representing 14% of those loaded onto the column, became tightly bound to the agarose-linked lectin, and the molecular weights of several of those proteins are reported. 6. Mannosyltransferase activities were measured in fractions highly enriched for mitochondria. 7. In the reactions, mannose was transferred from guanosine diphosphomannose to materials insoluble in 0.3% trichloroacetic acid or in chloroform:methanol (2:1). 8. The fractions also catalyzed the transfer of mannose to materials extractable in chloroform:methanol and which migrated with the Rf of dolichol phosphate on Silica Gel H. 9. Dolichol phosphate stimulated the transfer of mannose to those materials extractable in the organic solvents. 10. Marker enzyme analyses indicated that the mannosyl transferase activity in the mitochondrial fraction could not be accounted for entirely by contaminating microsomal membranes. 11. Although sialyltransferase activity was detected also in the mitochondrial fractions, the levels of the activity and the kinetics of the reactions indicated that Golgi membranes were most likely the sources of the enzyme.
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PMID:Mitochondrial biogenesis: do liver mitochondria contain glycoproteins and glycosyltransferases? 228 16

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