Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.99.7 (sialyltransferase)
 1,534 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rat liver beta-galactoside alpha-2,6-sialyltransferase and Vibrio cholerae sialidase were used with cytidine-5'-monophospho-N-acetyl-[3H]neuraminic acid (CMP-[3H]NeuAc) to specifically probe the distribution and sialylation state of Gal beta 1-4GlcNAc residues on N-linked saccharides on the surfaces of murine lymphocytes. The relative extent of exogenous sialyltransferase-mediated sialylation (per cellular protein) was thymocytes greater than T-cells greater than T-cell lymphoma (EL-4) greater than B-cells greater than B-cell lymphoma (AKTB-1b) greater than splenocytes. Prior desialylation increased exogenous resialylation by 23.8-, 13.1-, 7.1-, 7.9-, 7.0-, and 5.3-fold for splenocytes, B-cells, T-cells, EL-4, AKTB-1b, and thymocytes, respectively. Though numerous glycoproteins were labeled, the majority of the Gal beta 1-4GlcNAc residues were detected on a relatively small number of cell surface proteins, many of which are well-defined lymphocyte antigens. Gal beta 1-4GlcNAc residues on thymocytes were found to exist in an undersialylated state on T200 but not on other antigens (e.g., Thy-1). T200 was found to be fully sialylated on mature cells (i.e., hydrocortisone-resistant thymocytes and splenic T-cells), suggesting that its sialylation state is developmentally regulated. These studies indicate that the number, sialylation state, and polypeptide distribution of the penultimate structure, Gal beta 1-4GlcNAc, differ on N-linked saccharides on the surfaces of different lymphocyte populations.
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PMID:Surfaces of murine lymphocyte subsets differ in sialylation states and antigen distribution of a major N-linked penultimate saccharide structure. 213 33

Recent reports have suggested that the majority of the molecular traffic through the Golgi apparatus is comprised of recycling, rather than newly synthesized, molecules. To evaluate the importance of this recycling pathway in greater detail, we examined the internalization and recycling of cell surface glycoproteins on EL-4 cells, a murine T-cell lymphoma, using sialic acids as covalent markers. Sialic acids were removed from the surface of living cells by exhaustive treatment with Vibrio cholerae sialidase at 4 degrees C and shown to be derived primarily from glycoproteins (93%), with only a small amount from glycolipids (7%). Cells were recultured at 37 degrees C over time and monitored for the resialylation of the cell surface using a sensitive high pressure liquid chromatography adaptation of the thiobarbituric acid assay for sialic acids. The return of sialic acid to the cell surface was found to be contingent upon de novo protein synthesis indicating that the bulk of plasma membrane sialoglycoconjugates do not recycle to an endogenous sialyltransferase-containing compartment for oligosaccharide reprocessing. Identical results were found for K562 cells, a human erythroleukemia cell line. The movement of specific glycoproteins was followed using the enzyme rat liver alpha 2-6Gal beta 1-4GlcNAc sialyltransferase together with CMP-[3H]NeuAc as an impermeant probe of the cell surface. Surface sialoglycoproteins were internalized slowly, a process unaffected by cycloheximide treatment. Only a few of these internalized glycoproteins were found to return to a trans-Golgi compartment followed by recycling to the cell surface. Taken together, these data indicate that the majority of replacement of sialic acids on the cell surface is due to de novo synthesis of glycoproteins and that only a small number of glycoproteins recycle through a trans-Golgi compartment.
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PMID:Intracellular trafficking of cell surface sialoglycoconjugates. 318 95