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At least 19 recordsLinked to original sources
PubMed1989

O-acetylation and de-O-acetylation of sialic acids. Sialic acid esterases of diverse evolutionary origins have serine active sites and essential arginine residues.

We and others have recently described 9-O-acetyl-sialic acid esterase (9-O-Ac-SA esterase) activities that appear to be specific for removal of O-acetyl esters from the 9-position of naturally occurring sialic acids. We have now examined a variety of species for such enzymes and found them in vertebrates and higher invertebrates, but not in plants or in lower invertebrates. This evolutionary distribution correlates well with that of the sialic acids themselves. All of the 9-O-Ac-SA esterase activities tested were inhibited by diisopropyl fluorophosphate (DFP) in a dose-dependent fashion. This indicates that each of these enzymes has a serine active site similar to the well known serine esterases and serine proteases. Methyl esterification of the carboxyl group of 9-O-acetyl-N-acetylneuraminic acid significantly reduced the activity of all of the 9-O-Ac-SA esterases against the O-acetyl group. This indicates that each of these enzymes may recognize the negatively charged carboxyl group of the sialic acid. Enzymes that recognize anionic substrates frequently have an essential arginine residue (Riordan, J. F., McElvany, K. D., and Borders, C. L., Jr. (1977) Science 195, 884-886). We therefore studied the effects of the arginine-specific modifying reagents 2,3-butanedione and phenylglyoxal on 9-O-Ac-SA esterase activities from influenza C virus, human erythrocytes, rat liver, starfish gonads, and sea bass brain. All of these enzymes were inhibited in a dose-dependent fashion by both reagents, under conditions previously known to avoid nonspecific modification. In contrast, the typical serine proteases trypsin and kallikrein and the serine esterase acetylcholinesterase were not significantly affected, even by the highest concentrations of these reagents used. These data indicate that five 9-O-Ac-SA esterase activities from evolutionarily distinct origins all have serine active sites and essential arginine residues. We postulate that the arginine residue is involved in substrate recognition via the negatively charged carboxyl group of the sialic acids. Thus, these 9-O-Ac-SA esterase activities may be members of a previously undescribed class of serine esterase.

Acetylation↗
PubMed1990

[N-acetylneuraminic acid (sialic acid) as a tumor marker in head and neck cancers].

N-acetyl-neuraminic-acid (sialic acid) is a natural component of the cell surface. Cancer cells show a higher concentration of sialic acid in the cell membrane, and the serum also shows an elevated level of sialic acid. The concentration of sialic acid was measured in the serum of 76 new tumour patients and 113 previously treated patients who were clinically free of recurrence. The primary tumour was classified as T1-T4 according to the UICC classification. A further group consisted of patients with recurrent tumours. The values were compared with the sialic acid concentration in the sera of 63 healthy probands. Patients with manifest tumours showed an increased level of sialic acid that correlated with the extent of the tumour. The sialic acid level in 71% of patients with a recurrence lay above the upper limit of normal (82 mg/dl) recorded in the sera of healthy probands. The measurement of the serum sialic acid is a useful parameter for early detection of recurrence.

Biomarkers, Tumor↗
PubMed1985

Overproduction of N-acetylneuraminic acid (sialic acid) by sialuria fibroblasts.

Fibroblasts from the original sialuria patient are shown to contain high levels of free sialic acid, i.e., an average of 87 versus a normal average of 2 nmol/mg of protein. Gas liquid chromatography-mass spectrometry analysis confirmed that the accumulated material is N-acetylneuraminic acid. Addition of D(+) glucosamine (0-5 mM) to the media of these cells increased the intracellular free sialic acid concentrations from 74 to 137 nmol/mg protein. In contrast, normal cells treated in an identical manner maintained their normal free sialic acid level of less than 4 nmol/mg protein. Addition of 20 mM N-acetylmannosamine in place of glucosamine resulted in a marked increase in free sialic acid in both the patient and the control, i.e., increases of 157 (from 95 to 252) and 120 (from 3 to 123) nmol/mg protein, respectively. Finally, while normal cells in the presence of glucosamine accumulated high levels of uridine diphosphate N-acetylhexosamine, the patient's cells accumulated much lower amounts of this compound. It is concluded that the elevated sialic acid level in sialuria is due, at least in part, to overproduction of free N-acetylneuraminic acid. Indirect evidence is presented that this may result from either hyperactivity or increased levels of the enzyme (uridine diphosphate N-acetylglucosamine 2-epimerase) that has been shown in other tissues to convert uridine diphosphate N-acetylglucosamine to N-acetylmannosamine.

Cells, Cultured↗
PubMed1985

Accumulation of N-acetylneuraminic acid (sialic acid) in human fibroblasts cultured in the presence of N-acetylmannosamine.

Human skin fibroblasts incubated for 72 h in medium containing 10 mM N-acetyl-D-mannosamine accumulate material that yields a chromophore in the presence of thiobarbituric acid. This material was tentatively identified as free (unbound) sialic acid due to its reactivity with thiobarbituric acid prior to acid hydrolysis, its solubility in 10% trichloroacetic acid, its chromatographic properties on an anion-exchange column and its enzymatic susceptibility to acylneuraminate pyruvate-lyase. Mass spectrometry analysis established that the accumulated material was, in fact, N-acetylneuraminic acid. Loading studies demonstrated a linear relationship between the amount of N-acetylmannosamine in the medium and the level of sialic acid accumulating within the cells. Cells grown in the absence of N-acetylmannosamine contained an average of 5 nmol free sialic acid/mg protein, while cells cultured for 72 h in 20 mM amounts of this material contained an average of 156.3 nmol free sialic acid/mg protein. When the cells were removed from the N-acetylmannosamine-enriched medium and incubated in regular medium, more than 80% of the accumulated, intracellular sialic acid disappeared within the first 96 h. It was concluded from these data that normal fibroblasts cultured in medium enriched with N-acetylmannosamine store large amounts of N-acetylneuraminic acid and can thus serve as an excellent model for the study of both normal and abnormal sialic acid metabolism, transport, storage and/or metabolic (feedback) regulation in human tissue.

Biological Transport, Active↗
PubMed1989

Evidence for non-lysosomal storage of N-acetylneuraminic acid (sialic acid) in sialuria fibroblasts.

The results of the investigations reported here indicate that patients affected with the infantile sialic acid storage disorder (ISSD) and the original French sialuria patient suffer from distinct and fundamentally different disorders. While phase microscopy and immunochemical studies demonstrated abnormal storage within intracellular inclusions in ISSD cells, no morphological evidence of storage within any subcellular organelles was found in the sialuria cells. Moreover, comparative subcellular fractionation studies on gradients of colloidal silica showed the excess sialic acid in ISSD cells to be located within the light (buoyant) lysosomal fraction, while the excessive, free sialic acid in the sialuria cells was found in the cytoplasmic fraction with no increased storage within the lysosomal fractions. It is concluded that the sialic acid abnormalities in ISSD and the French type of sialuria are the result of very different biochemical and genetically unrelated abnormalities.

Fibroblasts↗
PubMed1980

Theoretical studies on the conformation of beta-D-N-acetyl neuraminic acid (sialic acid).

The possible conformations of sialic acid were analysed using semi-empirical potential functions. The solid state conformation has approx. 0.2 kcal/mol higher energy than the minimum energy conformation. These studies suggest that in solution sialic acid may exist preponderantly in two different conformations which differ in the orientation of the terminal hydroxymethyl group of glycerol side-chain. The present model is consistent with 1H- and 13C-NMR data, but differs from the earlier models.

Models, Chemical↗
PubMed1981

Turnover of free sialic acid, CMP-sialic acid, and bound sialic acid in rat brain.

Adult male rats were injected intraventricularly with N-[3H]acetylmannosamine. After different time intervals the rats were killed and free sialic acid, CMP-sialic acid, lipid- and protein-bound sialic acid were isolated from brain and the specific radioactivities determined. Maximal specific radioactivity was reached after approximately 4 h for CMP-sialic acid, after 10-12 h for free sialic acid and after approximately 42 h for lipid- and protein-bound sialic acid. After some days the specific radioactivities of all four pools were the same and decreased equally, with a calculated turnover rate of approximately 3.5 weeks. The conclusion was that this phenomenon was the result of reutilisation of sialic acid and/or precursors. Therefore, the calculated turnover is not the turnover of bound sialic acid, but merely the rate of leakage of sialic acid and/or precursors out of the brain, so that no real turnover can be measured by this method. The first few hours after injection the specific radioactivity of CMP-sialic acid rose above that of free sialic acid. It is supposed that a compartmentalization exists of free sialic acid. The newly synthesised sialic acid molecules are not secreted into the cytoplasmic pool but are preferentially used for the synthesis of CMP-sialic acid. The results and conclusions are discussed in view of the general problems concerning turnover measurements of glycoconjugates.

Animals↗
PubMed1984

New techniques for the investigation of structure and metabolism of sialic acids.

Sialic acid analysis in biological material including gangliosides is often confronted with the necessity to determine trace amounts of various N,O-substituted species. Therefore, techniques of high sensitivity and resolution are required, such as capillary gas-liquid chromatography (GLC) and high performance liquid chromatography (HPLC). Both methods in combination with mass spectrometry allow structural analysis of the different neuraminic acid derivatives. Thus, the number of natural sialic acids known so far has increased to more than 30, including non only saturated, but also 2,3-unsaturated and 2,7-anhydro-sialic acids. Furthermore, HPLC has proved to be especially useful for the study of enzyme reactions, as the sialic acids of enzyme assay mixtures in most cases can be analyzed without prior extensive purification or derivatization.

Animals↗
PubMed1998

O-acetylation of sialic acids.

Sialic acids can be acetylated at the 4, 7, 8 and/or 9 position. Biological roles of these substitutions have been missed until recently because of their low abundance and lability to conventional purification methods. The recent advances in the analysis of sialic acids have allowed to demonstrate that O-acetylation has a selective but widespread distribution. The metabolism of acetylated sialic acids is under the control of two groups of enzymes, O-acetyl transferases and 9-O-acetyl esterases. O-acetyl transferases are difficult to purify, and furthermore, attempts at expression cloning have failed in isolating the true 9-O-acetyl transferase cDNA. This explains that the regulation of the selective expression of O-acetylated sialic acid in not completely understood. Acetylation of sialic acid is expressed on the outer most part of the carbohydrate moiety of membrane and secreted glycoconjugates. This particular location explains why this modification is involved in cell/cell interactions and in the non-immune protection of mucosa.

Acetylation↗
PubMed1996

[Lipopolysaccharides containing sialic acid].

Sialic acids which are important constituents of animal tissue glycoconjugates are also present in antigens of some bacterial strains. Capsular polysaccharides with sialic acid have been extensively studied whereas little is known on lipopolysaccharides which contain sialic acid. The paper presents review of the data concerning structure of bacterial endotoxic lipopolysaccharides. Methodological peculiarities were described. Specially emphasized were endotoxins of Escherichia coli O24, O56, O104, Salmonella toucra O48, Citrobacter freundii O37 and Hafnia alvei strain PCM2386.

Bacterial Toxins↗
PubMedDate not supplied

An immobilized bienzyme system for assay of sialic acid.

Sialic acid has been assayed enzymatically by an immobilized two-enzyme system. The method includes cleavage of sialic acid to pyruvic acid by N-acetylneuraminic acid (NANA) aldolase and reduction of pyruvic acid by lactate dehydrogenase in the presence of NADH, which is followed photometrically at 349 nm. For the membrane preparation 5 units of lactate dehydrogenase and 1 unit of NANA-aldolase were used. The pH optimum of the reaction using potassium phosphate buffer was 7.0. This two-enzyme membrane remains 100% active for several weeks at 4 degrees C in the assay buffer and remains stable after performing experiments at 45 degrees C.

Animals↗
PubMed1978

Anti-inflammatory effect of sialic acid.

Sialic acid was shown to possess anti-inflammatory properties as measured by carrageenan-induced rat paw oedema and pleurisy tests. As the number of leukocytes mobilized was significantly reduced it was concluded that the inhibitory effect of sialic acid on leukocyte accumulation is responsible for the inhibition of exudate/oedema formation.

Animals↗