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1

The content of N-acetylneuraminic acid in glycoproteins of erythrocyte membranes in Moris hepatoma 5123 bearing rats

100%
Batko J., Karon H.
Acta Biochimica Polonica
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1994
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tom 41
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nr 1
Changes in the content of N-acetylneuraminic acid in rat erythrocyte membranes at different stages of experimental tumour (Morris hepatoma 5123) development were examined. Its content was lowered on the 30th and 40th day after transplantation of the tumour cells, as compared to the results for normal healthy rats. As a result of the tumour growth, the content of N-acetylgalactosamine, galactose and mannose in rat erythrocyte membranes became lowered, whereas that of glucose remained unchanged. The content of fucose was raised at early stage of tumour growth, and remained at this high level till the 40th day of experiment.
2

Glycophorin A in two patients with congenital dyserythropoietic anemia type I and type II is partly unglycosylated

84%
Zdebska E., Adamczyk-Poplawska M., Koscielak J.
Acta Biochimica Polonica
|
2000
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tom 47
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nr 3
Glycophorins A from erythrocyte membranes of two patients with congenital dyserythropoietic anemia type I and type II (CDA type I and II) were analyzed for carbohydrate molar composition employing a modification of the recently published method that allowed simultaneous determination of carbohydrates and protein in electrophoretic bands of glycoproteins separated by sodium dodecyl sulfate- polyacrylamide gel electrophoresis (Zdebska & Koscielak, 1999, Anal. Biochem., 275, 171-179). The modification involved a preliminary extraction of erythrocyte membranes with aqueous phenol, subsequent electrophoresis and analysis of the extracted glycophorins rather than electrophoresis and analysis of the glycophorin from intact erythrocyte membranes. The results showed a large deficit of N-acetylgalactosamine, galactose, and sialic acid residues in glycophorin A from patients with CDA type I and type II amounting to about 45% and 55 %, respectively. The results strongly suggest that glycophorin A in these patients is partly unglycosylated with respect to O-linked glycans. In addition, glycophorin A from erythrocytes of a patient with CDA II but not CDA I exhibited a significant deficit of mannose and N-acetylglucosamine suggesting that its N-glycosylation site was also partly unglycosylated.
3

Purification and characterization of GlcNAc-6-P 2-epimerase from Escherichia coli K92

84%
Ferrero M. A., Martinez-Blanco H., Lopez-Velasco F. F., Ezquerro-Saenz C., Navasa N., Rodriguez-Aparicio L. B.
Acta Biochimica Polonica
|
2007
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tom 54
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nr 2
N-Acetylmannosamine (ManNAc) is the first committed intermediate in sialic acid metabolism. Thus, the mechanisms that control intracellular ManNAc levels are important regulators of sialic acid production. In prokaryotic organisms, UDP-N-acetylglucosamine (GlcNAc) 2-epimerase and GlcNAc-6-P 2-epimerase are two enzymes capable of generating ManNAc from UDP-GlcNAc and GlcNAc-6-P, respectively. We have purified for the first time native GlcNAc-6-P 2-epimerase from bacterial source to apparent homogeneity (1 200 fold) using Butyl-agarose, DEAE-FPLC and Mannose-6-P-agarose chromatography. By SDS/PAGE the pure enzyme showed a molecular mass of 38.4 ± 0.2 kDa. The maximum activity was achieved at pH 7.8 and 37oC. Under these conditions, the Km calculated for GlcNAc-6-P was 1.5 mM. The 2-epimerase activity was activated by Na++ and inhibited by mannose-6-P but not mannose-1-P. Genetic analysis revealed high homology with bacterial isomerases. GlcNAc-6-P 2-epimerase from E. coli K92 is a ManNAc-inducible protein and is detected from the early logarithmic phase of growth. Our results indicate that, unlike UDP-GlcNAc 2-epimerase, which promotes the biosynthesis of sialic acid, GlcNAc-6-P 2-epimerase plays a catabolic role. When E. coli grows using ManNAc as a carbon source, this enzyme converts the intracellular ManNAc-6-P generated into GlcNAc-6-P, diverting the metabolic flux of ManNAc to GlcNAc.
4

Serum glycoproteins in patients with hypo- and hyperthyroidism

67%
Kucharz E. J., Olczyk K., Glowacki A., Duraj-Kassem M.
Acta Biochimica Polonica
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1993
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tom 40
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nr 1
5

N-acetylneuraminic acid, phosphate and thiol groups of pyruvate kinase isoenzymes from Morris hepatoma 7777 and normal rat liver

67%
Ignacak J., Guminska M.
Acta Biochimica Polonica
|
1997
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tom 44
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nr 2
The highest amount of N-acetylneuraminic acid (AcNeu) was found in pyruvate kinase isoenzyme L from normal rat liver (24 moles/mole of enzyme tetramer), with the highest electrophoretic mobility. On the other hand, isoenzyme M2 from Morris hepatoma 7777, with the lowest electrophoretic mobility, had the lowest AcNeu content (5 moles/mole of enzyme tetramer). This tumour isoenzyme M2 of pyruvate kinase was, however, characterised by the highest phosphate content (12 moles/mole protein), in comparison to isoenzyme L (3 moles/mole protein) or normal liver isoenzyme M2 (6 moles/mole protein). This could indicate a regulatory change caused by reversible enzyme phosphorylation and dephosphorylation or sialization and desialization. Despite these differences, the sum of the two negatively charged residues was lower in tumour pyruvate kinase isoenzyme M2, with the slowest migration rate, than in normal rat liver isoenzyme M2. Moreover, isoenzyme M2 from tumour material, in comparison with isoenzyme M2 from normal rat liver, had a twice as high content of thiol groups (20 moles/mole protein), especially of free and superficially located ones, than the isoenzyme M2 from normal liver (10 moles/mole protein). This may explain abnormal susceptibility of tumour isoenzyme M2 to stereospecific inhibition by exogenous L-cysteine, and indicate genetically dependent changes in amino-acid content of tumour enzyme which take place during cell tumourigenic transformation.
6
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The contribution of N-acetylneuraminic acid in the stabilization of micellar casein

67%
Minkiewicz P., Dziuba J., Muzinska B.
Polish Journal of Food and Nutrition Sciences
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1993
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tom 02
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nr 3
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