Studies on the enzymic N-acylation of amino sugars in the sheep colonic mucosa |
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| Authors: | A Allen and P W Kent |
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| Affiliation: | Department of Biochemistry, University of Oxford |
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| Abstract: | 1. d-2-(14)C]Glucose, 2-(14)C]acetate, hydroxy3-(14)C]pyruvate, 3-(14)C]pyruvate and U-(14)C]glycine were incorporated by surviving scrapings of sheep colonic mucosal tissue into glycoprotein. 2. d-2-(14)C]Glucose, 2-(14)C]acetate, incorporated hydroxy-3-(14)C]pyruvate and 3-(14)C]pyruvate resulted in labelling of each of the monosaccharide residues of the glycoprotein, namely N-glycollylneuraminic acid, N-acetylneuraminic acid, galactose, fucose, glucosamine and galactosamine. U-(14)C]Glycine was incorporated as glycyl and seryl residues of the glycoprotein. 3. Despite N-glycollylneuraminic acid being quantitatively the predominant sialic acid (N-glycollylneuraminic acid and N-acetylneuraminic acid were 8.5 and 5.2% by weight of the glycoprotein respectively) the corresponding ratio of the radio-active labelling from d-2-(14)C]glucose in N-glycollylneuraminic acid to that in N-acetylneuraminic acid was 1.00:7.27 (expressed as percentages of the total radioactivity in the glycoprotein). Neutral sugar, hexosamine and N-acetylneuraminic acid residues of the mucoprotein were each labelled to a similar extent. 4. Similarly, the ratio of the radioactivity in N-glycollylneuraminic acid to that in N-acetylneuraminic acid in the mucoprotein from tissue incubations with 2-(14)C]-acetate was 1.0:4.0. 5. Both 2-(14)C]acetate and 2-(14)C]glucose with whole tissue led to labelling of the N-glycollyl substituent and of the main nonose skeleton of the N-glycollylneuraminic acid. In whole-tissue incubations, 3-(14)C]pyruvate was also a precursor of radioactive N-glycollylneuraminic acid. 6. Hydroxy3-(14)C]-pyruvate and U-(14)C]glycine caused labelling of the carbohydrate and peptide residues of the glycoprotein, but did not give rise to labelling in the N-glycollylneuraminic acid residues. 7. With a wide variety of possible N-glycollyl precursors (fructose 6-phosphate, hydroxypyruvate, glycollate and chemically synthesized glycollyl-CoA) biosynthesis of N-glycollylglucosamine was not observed in cell-free preparations. |
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