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 intracellular site of sphingomyelin (SM) synthesis was examined in subcellular fractions from rat liver using a radioactive ceramide analog N-([1-14C]hexanoyl)-D-erythro-sphingosine. This lipid readily transferred from a complex with bovine serum albumin to liver fractions without disrupting the membranes, and was metabolized to radioactive SM. To prevent degradation of the newly synthesized SM to ceramide, all experiments were performed in the presence of EDTA to minimize neutral sphingomyelinase activity and at neutral pH to minimize acid sphingomyelinase activity. An intact Golgi apparatus fraction gave an 85-98-fold enrichment of SM synthesis and a 58-83-fold enrichment of galactosyltransferase activity. Controlled trypsin digestion demonstrated that SM synthesis was localized to the lumen of intact Golgi apparatus vesicles. Although small amounts of SM synthesis were detected in plasma membrane and rough microsome fractions, after accounting for contamination by Golgi apparatus membranes, their combined activity contributed less than 13% of the total SM synthesis in rat liver. Subfractions of the Golgi apparatus were obtained and characterized by immunoblotting and biochemical assays using cis/medial (mannosidase II) and trans (sialyltransferase and galactosyltransferase) Golgi apparatus markers. The specific activity of SM synthesis was highest in enriched cis and medial fractions but far lower in a trans fraction. We conclude that SM synthesis in rat liver occurs predominantly in the cis and medial cisternae of the Golgi apparatus and not at the plasma membrane or endoplasmic reticulum as has been previously suggested.
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PMID:Sphingomyelin synthesis in rat liver occurs predominantly at the cis and medial cisternae of the Golgi apparatus. 218 69

A sialyltransferase activity which catalyzes the synthesis of the trisialoganglioside GT1a from added disialoganglioside TD1a and CMP-N-acetylneuraminic acid has been demonstrated using a particulate fraction of 9-day-old embryonic chick brains. The enzyme exhibited optimum activity with the detergent Triton CF-54 and showed a broad pH optimum of 6.0 to 7.2. Ca2+ inhibited the reaction, whereas Mn2+, Mg2+, and EDTA had no effect. Slight elevations in activity were seen in the presence of Hg2+ or histone. The apparent Km for GD1a leading to GT1a was estimated to be 10(-3) M. When the monosialoganglioside, GM1, was used as the glycolipid substrate under conditions optimum for the synthesis of GR1a from GD1a, approximately 65% of the radioactive label was found in GD1a. However, about 50% of the remaining radioactivity was found in GT1a. The results suggest that the synthesis of GR1a could proceed via the sequence GM1 yields GD1a yields GT1a.
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PMID:In vitro biosynthesis of an isomer of brain trisialoganglioside, GT1a. 676 28

A sialyltransferase activity which catalyzes the synthesis of the tetrasialoganglioside GQ1b (N-acetylneuraminyl-N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]-galactosylglucosylceramide) from added trisialoganglioside GT1b (N-=acetylneuraminylgalactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]galactosylglucosylceramide) and CMP-N-acetyl[4-14C]neuraminic acid has been demonstrated using a membrane fraction of embryonic chick brain. Optimum enzymatic activity was obtained using the detergent Triton CF-54 at a pH of 6.6. Enzyme activity appeared unaffected by Ca2+, Mg2+, Mn2+, EDTA, or histone. A slight elevation in activity was seen in the presence of Hg2+. When the disialoganglioside GD1b (galactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]galactosylglucosylceramide) was used as the glycolipid substrate, approximately 15% of the radioactive label was found in GQ1b. When this GQ1b was subjected to a periodate oxidation-borohydride reduction, the distribution of radioactive label was consistent with GQ1b being the major tetrasialoganglioside product and that its synthesis could proceed via the sequence GD1b-GT1b-GQ1b.
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PMID:In vitro biosynthesis of the tetrasialoganglioside GQ1b. 705 68

A sensitive assay for sialyltransferase (STase activity extracted from gonococci with 0.5% Triton X100 was developed. Enzyme activity was optimal in the pH range 5.8-8.0 and was strongly inhibited by CMP, CDP and CTP, but not by other nucleotides, 10 mM Mg2+, Zn2+, Ca2+ or Mn2+, or by 18 mM EDTA. More than 90% of the activity was lost after 30 s at 67 degrees C. The apparent Vmax and apparent Km of the STase for cytidine 5'-monophospho-N-acetylneuraminic acid were 1.7 nmol of NANA incorporated/min/mg protein and 5.3 microM, respectively.
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PMID:Detection and some properties of the sialyltransferase implicated in the sialylation of lipopolysaccharide of Neisseria gonorrhoeae. 832 54

A method for the assay of CMP-NeuAc:(NeuAc alpha 2-->8)n (colominic acid) sialyltransferase activity was developed. Using a 1-day-old rat brain membrane fraction as an enzyme preparation optimal activity was obtained at pH 6.5, 0.3% Triton X-100, and 5 mM MnCl2. However, no absolute cation requirement was found as EDTA only partially inhibited the activity. Within a concentration range of 0.3-3 mg colominic acid (which consists of a mixture of oligomers of alpha 2-->8-linked sialic acid) per 50 microliters a V of 0.61 nmol per mg protein h-1 was estimated while a half-maximal reaction velocity was obtained at a concentration of 1.75 mg per 50 microliters. High performance anion-exchange chromatography of the radioactive products formed in the reaction showed that sialic acid oligomers ranging in size from a degree of polymerization (DP) of 2 up to at least DP 9 could serve as acceptor substrates. Comparison of the acceptor properties of DP 3 and DP 6 showed that the larger oligomer was acted upon with a 10-fold higher efficiency. Periodate oxidation of the products followed by reduction and hydrolysis yielded the C7 analogue of NeuAc as the only radioactive product, indicating that under the conditions of the assay only a single sialic acid residue was introduced into the acceptor molecules. Using the assay it appeared that in rat brain the activity of this sialyltransferase decreased six-fold during postnatal development to the adult stage. The assay method was also applied to lysates of several neuroblastoma and small cell lung tumour cell lines, which differ in the expression of polysialic acid as well as of the neural cell adhesion molecule NCAM, a major carrier of this polymer. Activity of the sialyltransferase appeared to be correlated with the expression of polysialic acid present on NCAM. These results indicate that this sialyltransferase might function in the process of poly-sialylation.
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PMID:CMP-NeuAc:(NeuAc alpha 2-->8)n (colominic acid) sialyltransferase activity in rat brain and in tumour cells that express polysialic acid on neural cell adhesion molecules. 874 61

Photobacterium damsela alpha2,6-sialyltransferase was cloned as N- and C- His-tagged fusion proteins with different lengths (16-497 aa or 113-497 aa). Expression and activity assays indicated that the N-terminal 112 amino acid residues of the protein were not required for its alpha2,6-sialyltransferase activity. Among four truncated forms tested, N-His-tagged Delta15Pd2,6ST(N) containing 16-497 amino acid residues had the highest expression level. Similar to the Delta15Pd2,6ST(N), the shorter Delta112Pd2,6ST(N) was active in a wide pH range of 7.5-10.0. A divalent metal ion was not required for the sialyltransferase activity, and the addition of EDTA and dithiothreitol did not affect the activity significantly.
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PMID:N-Terminal 112 amino acid residues are not required for the sialyltransferase activity of Photobacterium damsela alpha2,6-sialyltransferase. 1798 25