Analysis of N,O-acylated neuraminic acids by high-performance liquid anion-exchange chromatography

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Presence of sialic acid in prothoracic glands of Galleria mellonella (Lepidoptera)

The presence of sialic acid (SA) in prothoracic glands (PGs) of Galleria mellonella was determined by the methods of electron microscopy (EM), histochemistry, spectrophotometry (SP) and electronic ionization (EI)-mass spectroscopy. Histochemical observations were carried out by the cationic dye ruthenium red (RR), staining with and without neuraminidase digestion in the larval stage. Neuraminidase-sensitive SA was demonstrated by the decrease in the amount of RR-binding following neuraminidase digestion. The total amount of SA was found to be 0.09016 mg g(-1) in dry tissue by spectrophotometric determination. EI-mass spectroscopy results confirmed the EM and SP observations. The fragmentation scheme derived from EI-mass analysis exhibited the presence of the lactonized form of Neu5Gc7, 9Ac(2). On the basis of the various pieces of evidence described above, it was firmly concluded that Neu5Gc7, 9Ac(2) molecules were present in PGs of G. mellonella.

Isolation and properties of two sialate-O-acetylesterases from horse liver with 4- and 9-O-acetyl specificities

Sialate-O-acetylesterase was purified almost 900-fold from particle-free supernatants of horse liver by gel filtration, ion-exchange chromatography and isoelectric focussing. The native enzyme on gel filtration exhibits a molecular weight of 54,000 Da. It was separated by isoelectric focussing into two forms with pI values of 4.8 and 5.7, respectively. The esterase with a lower pI hydrolyses only 9-O-acetyl groups from sialic acids (K(M) 1.1 mM), while that with the higher pI esterifies both 4- and 9-O-acetylated monosaccharides at similar rates (K(M) 0.3 M and 1.3 mM, respectively). Both forms are inactive with 7-O-acetylated N-acetylneuraminic acid. Enzyme assays were carried out at the pH optimum (pH 8.4-8.6) using free O-acetylated sialic acids followed by direct analysis of the reaction products by isocratic anion-exchange HPLC. Glycosidically bound sialic acids can also be de-O-acetylated. Horse liver esterase seems to be an essential enzyme for the catabolism of 4-O-acetylated sialoglycoconjugates, since sialidase from this tissue cannot act on 4-O-acetylated sialic acids.

Determination of sialic acids in biological fluids using reversed-phase ion-pair high-performance liquid chromatography

A simple, rapid and sensitive reversed-phase ion-pair high-performance liquid chromatographic method for the determination of N-acetylneuraminic acid and 2-deoxy-2,3-dehydro-N-acetylneuraminic acid in biological fluids is described. Determination of N-acetylneuraminic acid released by acidic hydrolysis, in serum, urine and saliva, and 2-deoxy-2,3-dehydro-N-acetylneuraminic acid in urine, without hydrolysis, was accomplished by injecting the sample without derivatization, into the chromatograph. Measurements were carried out isocratically within 6 min using a C18 column and a mobile phase of aqueous solution of triisopropanolamine, as ion-pair reagent, 60 mM, pH 3.5 at room temperature with UV absorbance detection. The present method is reported for the first time for the determination of sialic acids in biological fluids. Recoveries in serum, urine and saliva ranged from 90 to 102% and the limits of detection were 60 nM and 20 nM for the two sialic acids, respectively. The method has been applied to normal and pathological sera from patients with breast, stomach, colon, ovarian and cervix cancers, to normal urine and urine from patient with sialuria and to normal saliva.

High-resolution thin-layer chromatography of gangliosides

In this review an updated overview of current improvements on thin-layer chromatography (TLC) of gangliosides over the past decade is provided. Basic general techniques and special advice is given for successful separation of glycosphingolipids. New approaches concerning continuous and multiple development, and several preparative TLC methods are also included. Emphasis is placed on TLC immunostaining and related techniques, i.e. practical applications of carbohydrate-specific antibodies, toxins and bacteria, viruses, lectins and eukaryotic cells. Thus, this review on ganglioside TLC summarizes its power as an analytical tool for a wide range of purposes.

Analysis of glycoproteins, glycopeptides and glycoprotein-derived oligosaccharides by high-performance capillary electrophoresis

Recent developments in the analysis of glycoproteins by high-performance capillary electrophoresis are reviewed, with emphasis on their carbohydrate chains. Glycoforms of glycoproteins were directly separated from each other by careful optimization of the analytical conditions. Glycopeptides in tyrptic digests were separated and the peptides carrying glycosylation sites were differentiated from others. Released oligosaccharide chains were separated from each other by direct or modified zone electrophoresis and directly detected by measuring the UV absorption at a low wavelength. Precolumn derivatization by various methods extended the utility of both the separation mode and detection technique. Dual mode analysis after derivatization permitted reliable identification and quantification without references.

Elevation of ratio of urinary N-acetylneuraminlactose to free sialic acid in some advanced cancer patients

We estimated the levels of free sialic acid and sialylated oligosaccharides excreted in the urine of normal donors (n = 10) and patients with gastric cancer (n = 6) and colorectal cancer (n = 4). The total sialic acid level in cancer patients was similar to that in normal donors. However, the ratios of glycosidically bound sialic acids to free sialic acid were higher in some advanced cancer patients than in the normal donors. A major component of sialylated oligosaccharides was N-acetylneuraminyl alpha (2-->3) lactose. The elevation of the urinary ratio of this sialylated oligosaccharide to free sialic acid observed in some advanced cancer patients in this study may reflect the elevation of sialyltransferase activity in tumor tissues.

Measurement of sialic acid in serum and urine: clinical applications and limitations

Many recent studies have examined the sialic acid content of serum or urine in various pathological states. We have briefly reviewed the substances which contribute to the observed total sialic acid concentration, and given an overview of assay methods used. Three major areas of clinical interest in sialic acid metabolism are discussed. Serum total sialic acid, 'lipid-bound' and 'protein bound' sialic acid have all been proposed as tumour markers; but the usefulness of any of these tests is severely limited by changes due to accompanying inflammatory processes. Serum total sialic acid is not a valuable simple marker of an acute phase response. Urinary free and bound sialic acid measurements should be included in screening protocols for inherited disorders of lysosomal metabolism. Current developments in research and potential applications within the clinical biochemistry laboratory are briefly discussed.

Determination of sialic acids in human serum by reversed-phase liquid chromatography with fluorimetric detection

A simple, rapid and highly sensitive reversed-phase liquid chromatographic method has been developed for the determination of sialic acids in human serum. The sialic acids, released by hydrolysis of serum, are converted in borate buffer with malononitrile to highly fluorescent compounds. The reaction mixture is separated isocratically within 5 min using an octadecyl-bonded silica column and a mobile phase of methanol and ammonium acetate buffer (15:85, v/v; pH 5.5). Measurement of the fluorescence intensity of the reaction mixture at 434 nm with irradiation at 357 nm allowed determination of 30-1000 ng/ml of sialic acids with high reproducibility. The limit of detection was 2 ng/ml. Intra-day and inter-day coefficients of variation for assaying 300 ng/ml N-acetylneuraminic acid (NANA) were 1.5% (n = 9) and 2.6% (n = 7), respectively. The recoveries of NANA were 98.5-101.1% for serum. The method has been used for clinical determinations.

Measurement of N-acetylneuraminic acid in human serum and urine by high performance liquid chromatography with chemiluminescence detection

A highly sensitive method for the determination of N-acetylneuraminic acid in human serum and urine is investigated. This method employs high performance liquid chromatography with chemiluminescence detection. N-Acetylneuraminic acid, released by hydrochloric acid hydrolysis of serum and urine, and N-glycolylneuraminic acid (internal standard) are converted into chemiluminescent derivatives with 4,5-diaminophthalhydrazide dihydrochloride, a chemiluminescence derivatization reagent for alpha-keto acids. The derivatives are separated within 35 min on a reversed phase column, TSKgel ODS-120T, with isocratic elution, followed by chemiluminescence detection; the chemiluminescence is produced by the reaction of the derivatives with hydrogen peroxide in the presence of potassium hexacyanoferrate(III) in alkaline solution. The detection limit for N-acetylneuraminic acid is 9 fmol (signal-to-noise ratio = 3). This sensitivity permits precise determination of N-acetylneuraminic acid in 10 nL of serum or 50 nL of urine. The method is applied to the determination of the N-acetylneuraminic acid in human sera from normal subjects and cancer patients and in normal urine.

An improved method for preparation of perbenzoylated ganglioside-derived sialic acids and nanogram detection of N-acetyl- and N-glycolylneuraminic acid by high performance liquid chromatography

An improved method for the preparation of perbenzoylated ganglioside-derived sialic acids is described. After mild acid hydrolysis, isolation of sialic acids can be achieved by Folch partition (Method A) or by anion exchange chromatography (Method B). Perbenzoylated sialic acids were freed from benzoylation reagents by a second Folch partition. Total recoveries of both methods were found to be greater than or equal to 90%, calculated from metabolically labelled gangliosides. Derivatized N-acetylneuraminic and N-glycolylneuraminic acids were separated and quantified by isocratic high performance liquid chromatography using a RP18 column as the stationary phase and methanol:water (8:2) as the mobile phase. Both sialic acids were completely separated and eluted as single peaks within 15 min, monitored by UV detection. As little as 20 ng of neuraminic acid could be detected, the detector being linear up to 5 micrograms tested.

Occurrence of sialic acids in Drosophila melanogaster

Sialylated oligosaccharides, which are cell type-specific and developmentally regulated, have been implicated in a variety of complex biological events. Their broad functional importance is reflected by their presence in a wide variety of phyla extending from Echinodermata through higher vertebrates. Here, sialic acids are detected throughout development in an insect, Drosophila. Homopolymers of alpha 2,8-linked sialic acid, polysialic acid, are developmentally regulated and only expressed during early Drosophila development.

Use of influenza C virus for detection of 9-O-acetylated sialic acids on immobilized glycoconjugates by esterase activity

An overlay and a solid-phase assay are presented which allow the specific detection of 9-O-acetylated sialic acids on sialoglycoconjugates immobilized on microtiter plates, nitrocellulose or separated on thin-layer chromatograms. The assay takes advantage of two different biological properties of influenza C virus, its high-affinity binding to 9-O-acetylated sialic acids and its sialate 9-O-acetylesterase that is used for detection of bound virus with fluorogenic or chromogenic substrates. Though simple and rapid, the assay is highly sensitive with a detection limit of 65 fmol 9-O-acetylated sialic acid in 9-O-acetylated ganglioside GD1a. Influenza C virus is able to bind to a wide spectrum of sialoglycoconjugates like mucins, serum glycoproteins or gangliosides containing naturally or synthetically O-acetylated sialic acids. 9-O-Acetyl-N-glycoloylneuraminic acid can also function as a high-affinity receptor determinant for influenza C virus. While the acetyl ester at the 9 position is essential for virus binding in all cases, a 4-O-acetyl group is not recognized. In addition to alpha(2.3) or alpha(2.6) bonds, 9-O-acetyl-N-acetylneuraminic acid in alpha(2.8) linkage to N-acetylneuraminic acid is also functionally active.

Nature and biosynthesis of sialic acids in the starfish Asterias rubens. Identification of sialo-oligomers and detection of S-adenosyl-L-methionine: N-acylneuraminate 8-O-methyltransferase and CMP-N-acetylneuraminate monooxygenase activities

Mass spectrometric and NMR spectroscopic analyses of bound sialic acids from the starfish Asterias rubens revealed the presence of N-acetylneuraminic acid (4%), N-acetyl-8-O-methylneuraminic acid (12%), N-acetyl-9-O-acetyl-8-O-methylneuraminic acid (less than 1%), N-glycoloylneuraminic acid (19%), N-glycoloyl-8-O-methylneuraminic acid (47%), and N-glycoloyl-9-O-acetyl-8-O-methylneuraminic acid (18%). Analysis of sialo-oligomeric material, obtained after mild acid hydrolysis, demonstrated that N-glycoloyl-8-O-methylneuraminic acid can occur as di- and tri-oligomers, linked through the anomeric center and the N-glycoloyl moiety, Neu5Gc8Me-alpha(2----O5)-Neu5Gc8Me and Neu5Gc8Me-alpha(2----O5)-Neu5Gc8Me-alpha (2----O5)-Neu5Gc8Me. Studies on the biosynthesis of N-acyl-8-O-methylneuraminic acid in A rubens, using the tracer S-adenosyl-L-[methyl-14C]methionine, showed that N-acylneuraminate 8-O-methyltransferase activity was present predominantly in the membrane fraction. CMP-N-acetylneuraminic acid monooxygenase activity was found in the soluble protein fraction, in agreement with investigations on the corresponding vertebrate enzyme.

Isoforms of turkey prolactin: evidence for differences in glycosylation and in tryptic peptide mapping

1. Three isoforms of turkey pituitary prolactin have been isolated, including a nonglycosylated isoform of 22,500 mol. wt and two glycosylated isoforms of 24,500 mol. wt. 2. The glycosylated turkey prolactins differed in carbohydrate composition, with one isoform apparently containing only O-linked carbohydrate. 3. Tryptic peptide maps showed a few peptides distinctly different among the three prolactin isoforms. 4. Amino acid sequencing of the first 40 residues of the three prolactin isoforms showed arginine at position 24 and histidine at position 27, for the nonglycosylated form, but no identifiable amino acids were detected at this position for the glycosylated isoforms.

Sialate O-acetylesterases: key enzymes in sialic acid catabolism

Sialate 9(4)-O-acetylesterases (EC 3.1.1.53) have been isolated from equine liver, bovine brain and influenza C virus. In this latter case, the esterase represents the receptor-destroying enzyme of the virus. The kinetic properties of these enzymes were determined with Neu5,9Ac2 and in part with 4-methylumbelliferyl acetate and Neu5,9Ac2-lactose. The Km values vary between 0.13 and 24 mM and the Vmax values from 0.55 to 11 U/mg of protein. The pH optima are in the range of 7.4-8.5, the molecular masses at 56,500 and 88,000 Da. In addition to a fast hydrolysis found for aromatic acetates, such as 4-methylumbelliferyl acetate or 4-nitrophenyl acetate, N-acetyl-9-O-acetylneuraminic acid is de-O-acetylated at the highest relative rate. Other substituents at the 9-position, such as lactoyl residues, or acetyl groups at other positions within the side chain are not hydrolyzed. Neu4,5Ac2, however, is a substrate for all 3 enzymes. The hydrolysis rates of this ester function, which renders sialic acids resistant to the action of sialidases, vary from 3 to 100% relative to Neu5,9Ac2. Whereas Neu5,9Ac2-lactose is hydrolyzed by the bovine and viral esterases, other O-acetylated sialic acids in glycoconjugates are only attacked by the enzyme from influenza C virus and not by that from bovine brain. The esterase from horse liver also releases 4-O-acetyl groups from equine submandibular gland mucin. By incubation with appropriate substrates and inhibition studies, carboxylesterase, amidase and choline esterase activities were excluded, as well as the cleavage of other acyls, e.g., butyryl groups. Thus, the enzymes investigated belong to the acetylesterases.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations of acyl-neuraminic acids on T-lymphocytes in cases of melanoma

Content and distribution of the different sialic acids on human lymphocytes, isolated from 7-10 ml of fresh human blood, were determined using microanalytical methods, such as HPLC and a colorimetric test. Comparison of the data of patients with melanoma with those of healthy persons shows an evident increase of the sialic acid content combined with a shift of the sialic acid distribution to higher O-acetylated derivatives.

Natural occurrence and preparation of O-acylated 2,3-unsaturated sialic acids

Three O-acylated, unsaturated sialic acids, N-acetyl-9-O-acetyl-, N-acetyl-9-O-lactoyl-, and 2-deoxy-N-glycoloyl-9-O-lactoyl-2,3-didehydroneuraminic acid (5-acetamido-9-O-acetyl-, 5-acetamido-9-O-lactoyl-, and 2,6-anhydro-3,5-dideoxy-5-glycoloylamido-9-O-lactoyl-D-glycero-D-g alacto-non-2- enonic acid) were isolated from urine or submandibular glands of rat, pig, and cow. Mass spectrometric evidence for the existence of 2,3-unsaturated 9-O-acetyl-N-glycoloylneuraminic acid in porcine urine was also obtained. The sialic acids were purified by dialysis, gel- and ion-exchange chromatography, and preparative thin-layer chromatography. They were analyzed by thin-layer chromatography, high-pressure liquid chromatography, and capillary gas-liquid chromatography-mass spectrometry. For comparison, O-acetylated unsaturated sialic acids were synthesized.

Maturational changes in terminal glycosylation of small intestinal microvillar proteins in the rat

Studies were performed to identify rat intestinal microvillar proteins which undergo changes in terminal glycosylation during postnatal development. Pulse-labeling with [3H]fucose or N-[3H]acetylgalactosamine showed significantly higher incorporation into purified microvillar membranes of weanling than suckling rats. In contrast, the incorporation of [3H]sialic acid after pulse-labeling with N-[3H]acetylmanosamine was higher in suckling rats. SDS-polyacrylamide gel electrophoresis revealed these developmental differences in radioactive sugar incorporation to involve mainly proteins above Mr 90,000. 125I-labeled peanut lectin autoradiography revealed an Mr greater than 330,000 binding protein in suckling rats. Neuraminidase treatment of the membranes revealed the presence of sialyl-substituted sites in this protein in suckling, weaning and weanling animals, but the unmasking of sites decreased with advancing maturation. 125I-labeled Ulex europeus I autoradiography showed marked increases in binding of this lectin to Mr 66,000, 92,000, 130,000, 150,000 and greater than 330,000 proteins from weaning to weanling periods. Similar age-related increases in soybean lectin binding to Mr 130,000-150,000, and greater than 330,000 proteins were demonstrated by affinity chromatography. The Mr values of the major lectin-binding proteins were close to those reported for several hydrolases (trehalase, alkaline phosphatase, sucrase-isomaltase and glucoamylase). Comparison of the Coomassie blue-stained electrophoretograms from each age-group against the corresponding autoradiograms of lection-binding proteins led us to conclude that, while the content of these proteins in the membrane achieve their mature levels at or before weaning, their terminal glycosylation (desialylation, fucosylation, N-acetylgalactosamination) is not fully established until later development.

Fluorometric high-performance liquid chromatography of N-acetyl- and N-glycolylneuraminic acids and its application to their microdetermination in human and animal sera, glycoproteins, and glycolipids

A simple, rapid, and highly sensitive high-performance liquid chromatographic method is described for the determination of N-acetyl- and N-glycolylneuraminic acids in human and animal sera, glycoproteins, and glycolipids. The neuraminic acids, released by acid hydrolysis of these biological samples, are converted in dilute sulfuric acid with 1,2-diamino-4,5-methylene-dioxybenzene, a fluorogenic reagent for alpha-keto acids, to highly fluorescent derivatives. The derivatives are separated within 12 min on a reversed-phase column (Radial-Pak cartridge C18) with an isocratic elution and detected fluorometrically. The detection limits are 25 fmol (7.7 pg) for N-acetylneuraminic acid and 23 fmol (7.5 pg) for N-glycolylneuraminic acid in a 10-microliter injection volume at a signal-to-noise ratio of 2. This method permits precise determination of the neuraminic acids in 5 microliter of human and animal sera or in 0.25-2.5 micrograms of glycoproteins and glycolipids.

N-acetyl-9-O-acetylneuraminic acid, the receptor determinant for influenza C virus, is a differentiation marker on chicken erythrocytes

Erythrocytes from chicken of different age were analysed for their agglutinability by influenza C virus, which has been shown recently to use N-acetyl-9-O-acetylneuraminic acid as a high-affinity receptor determinant for the attachment to cells. Only with birds not younger than six days complete agglutination of the erythrocytes was observed. The hemagglutination titer which was initially low reached its maximum value at the age of about 20 days. Sialic acid was isolated from erythrocytes, purified and analysed by colorimetry, thin-layer chromatography, high-performance liquid chromatography, and gas-liquid chromatography-mass spectrometry. The sialic acid content of erythrocytes from one-day old and adult chicken was 21 micrograms and 18 micrograms sialic acid/ml packed erythrocytes, respectively. While N-acetylneuraminic acid was the major type of sialic acid on erythrocytes from both one-day old and adult chicken, N-acetyl-9-O-acetylneuraminic acid was only detected on red blood cells from adult animals accounting for 30-40% of total sialic acid. These results indicate that N-acetyl-9-O-acetylneuraminic acid, in addition to serving as a receptor determinant for influenza C virus, represents a developmental marker on chicken erythrocytes.

Migration of O-acetyl groups in N,O-acetylneuraminic acids

Highly purified N-acetyl-4-O-acetylneuraminic acid (Neu4,5Ac2), N-acetyl-7-O-acetylneuraminic acid (Neu5,7Ac2) and N-acetyl-7,9-di-O-acetylneuraminic acid (Neu5,7,9Ac3) were used to study spontaneous migrations of acetyl groups between hydroxyl groups. The techniques applied involved thin-layer chromatography, gas-liquid chromatography/mass spectrometry, high-performance liquid chromatography and 360-MHz 1H-NMR spectroscopy. It was found that at pH values at which no significant de-O-acetylation is observed: (a) Neu5,7Ac2 can easily be transformed into Neu5,9Ac2, (b) Neu5,7,9Ac3 yields an equilibrium of Neu5,7,9Ac3 and Neu5,8,9Ac3 in a molar ratio of approximately 1:1, and (c) Neu4,5Ac2 does not give rise to O-acetyl migrations. The importance of these findings is discussed in terms of the biosynthesis of O-acetylated sialic acids.

Separation of anionic oligosaccharides by high-performance liquid chromatography

We have developed methods for rapid fractionation of anionic oligosaccharides containing sulfate and/or sialic acid moieties by high-performance liquid chromatography (HPLC). Ion-exchange HPLC on amine-bearing columns (Micropak AX-10 and AX-5) at pH 4.0 is utilized to separate anionic oligosaccharides bearing zero, one, two, three, or four charges, independent of the identity of the amnionic moieties (sulfate and/or sialic acid). Ion-exchange HPLC at pH 1.7 allows separation of neutral, mono-, di-, and tetrasialylated, monosulfated, and disulfated oligosaccharides. Oligosaccharides containing three sialic acid residues and those bearing one each of sulfate and sialic acid, however, coelute at pH 1.7. Since the latter two oligosaccharide species separate at pH 4.0, analysis at pH 4.0 followed by analysis at pH 1.7 can be utilized to completely fractionate complex mixtures of sulfated and sialylated oligosaccharides. Ion-suppression amine adsorption HPLC has previously been shown to separate anionic oligosaccharides on the basis of net carbohydrate content (size). In this study we demonstrate the utility of ion-suppression amine adsorption HPLC for resolving sialylated oligosaccharide isomers which differ only in the linkages of sialic acid residues (alpha 2.3 vs alpha 2.6) and/or location of alpha 2,3- and alpha 2,6-linked sialic acid moieties on the peripheral branches of oligosaccharides. These two methods can be used in tandem to separate oligosaccharides, both analytically and preparatively, based on their number, types, and linkages of anionic moieties.

Analysis of sialidase and N-acetylneuraminate pyruvate-lyase substrate specificity by high-performance liquid chromatography

A rapid and sensitive assay by high-performance liquid chromatography for determination of the activity and substrate specificity of sialidase (EC 3.2.1.18) and N-acetylneuraminate lyase (EC 4.1.3.3) is described. Sialic acids were separated on a strong anion-exchange resin using 0.75 mM sodium sulfate as elution medium. This method allows the determination of a minimum amount of 200 pg (0.6 pmol) of sialic acid. Usually the enzyme mixtures were directly applied to the column without prior purification of substrates and products. The action of sialidase was studied either by the decrease of sialyllactose concentration or by the amount of sialic acid liberated. The relative hydrolysis rates of N-acetylneuraminyl-alpha(2-3)-lactose, N-glycolylneuraminyl-alpha(2-3)-lactose, N-acetylneuraminyl-alpha(2-6)-lactose, N-acetyl-9-O-acetylneuraminyl-alpha(2-3)-lactose, and N-acetyl-4-O-acetylneuraminyl-alpha(2-3)-lactose by Vibrio cholerae sialidase were 100, 88, 25, 12, and 0, respectively. The activity of N-acetylneuraminate lyase from Clostridium perfringens was determined by measuring the rate of disappearance of sialic acids or the formation of acylmannosamines, which is possible in the same chromatogram. Relative cleavage rates of N-acetylneuraminic acid, N-glycolylneuraminic acid, N-acetyl-9-O-acetylneuraminic acid, N-acetyl-7-O-acetylneuraminic acid, and N-acetyl-4-O-acetylneuraminic acid were found to be 100, 67, 24, 3, and 0, respectively. Comparison of the substrate specificities shows that substituents on the neuraminic acid molecule influence the reactions of both enzymes in a similar way.

Detection of sialuria by cation-exchange high-performance liquid chromatography

A simple and selective method for the detection of sialuria by high-performance liquid chromatography is described. The urine sample (2 ml) is purified using a C18 cartridge or ion-exchange chromatography, and free N-acetylneuraminic acid is separated on an Aminex HPX-87 cation-exchange column using 3 mM sulphuric acid as the mobile phase. The retention time of N-acetylneuraminic acid is ca. 8 min and the detection limit ca. 1 mumol/l. The within-day coefficient of variation is less than 4.9% and the day-to-day coefficient of variation is less than 5.6%. The method was tested on twenty normal individuals and four sialuria patients.

Sialoglycoproteins and sialic acids of Plasmodium knowlesi schizont-infected erythrocytes and normal rhesus monkey erythrocytes

The effects of malaria infection on RBC sialic acids and sialoglycoproteins were studied with asexual blood-stage infections of Plasmodium knowlesi in rhesus monkeys. Glycoprotein radio-isotope labelling methods were used to compare the sialoglycoproteins of normal RBC and P. knowlesi schizont-infected RBC (SI-RBC). Tritiation of glycoproteins from SI-RBC with the standard sialidase + galactose oxidase/NaB3H4 method or standard periodate/NaB3H4 method was significantly decreased when compared to normal RBC. However, tritium uptake into glycoproteins was normal when SI-RBC were treated with 5-fold higher concentrations of both enzymes in the first labelling method, or with a 5-fold increase in the molar ratio of periodate to sialic acid in the second method. The mobility of tritiated host cell glycoproteins on SDS-polyacrylamide gels was identical for SI-RBC and normal RBC. New bands, possibly glycoproteins, of 230, 160, 90, 52, and 30 kDa were detected after labelling SI-RBC by the modified periodate/NaB3H4 method. Sialic acid analysis of normal rhesus monkey RBC (62 micrograms/10(10) RBC) revealed that 46% of the total sialic acid was N-glycolylneuraminic acid, 33% was N-acetyl-9-O-acetylneuraminic acid, and the remainder N-acetylneuraminic acid. SI-RBC collected either directly from infected monkeys or after in vitro culture of ring-infected RBC in horse serum, had increased total sialic acid (126 or 115 micrograms/10(10) RBC, respectively). The sialic acid content of infected RBC must increase during parasite development since RBC infected with ring-stage P. knowlesi had the same content as normal RBC. There was no significant difference in the ratio of the three sialic acids of SI-RBC and normal RBC. In contrast, the uninfected RBC from infected blood of different monkeys showed marked variation in sialic acid composition and generally had a lower sialic acid content than normal RBC.

Highly sensitive determination of N-acetyl- and N-glycolylneuraminic acids in human serum and urine and rat serum by reversed-phase liquid chromatography with fluorescence detection

A simple, rapid and highly sensitive high-performance liquid chromatographic method for the determination of N-acetyl- and N-glycolylneuraminic acids in serum and urine is described. The neuraminic acids, released by hydrolysis of serum and urine, are converted in dilute sulphuric acid with 1,2-diamino-4,5-dimethoxybenzene, a fluorogenic reagent for alpha-keto acids, to highly fluorescent derivatives. The derivatives are separated isocratically within 8 min by reversed-phase chromatography using a Radial-Pak cartridge C18 column and detected fluorimetrically. The limit of detection is 40 fmol (12 pg) for both neuraminic acids in 10-microliters injection volume [0.3 nmol (90 ng)/ml) of serum or urine]. This sensitivity permits the precise determination of the neuraminic acids in 5 microliters of serum or urine. The method was applied to the determination of the neuraminic acids in sera from normal subjects and cancer patients, normal urine and rat serum.

Structural parameters and natural occurrence of 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid

2-Deoxy-2,3-didehydro-N-glycoloylneuraminic acid has been found to occur in porcine, bovine and equine submandibular glands as well as in the urine of pig, horse and rat. This novel, unsaturated sialic acid was isolated by gel filtration and ion-exchange chromatography. Final purification was achieved by column chromatography or by preparative thin-layer chromatography on cellulose. The structural analysis was performed by combined capillary gas-liquid chromatography/mass spectrometry. The various data were compared with those from synthetic 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid. Besides of the unsaturated N-glycoloylated sialic acid, also the corresponding N-acetylated derivative was present in the materials analyzed. The inhibitory effect of 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid on Vibrio cholerae sialidase using N-acetylneuraminyl-(alpha 2----3)-lactose as substrate is slightly higher (50% inhibition at 10 microM) when compared with 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (50% inhibition at 15 microM).

Metabolic labeling of sialic acids in tissue culture cell lines: methods to identify substituted and modified radioactive neuraminic acids

The parent sialic acid N-acetylneuraminic acid can be modified or substituted in various ways, giving rise to a family of more than 25 compounds. The definitive identification of these compounds has previously required isolation of nanomole amounts for mass spectrometry or NMR. We have explored the possibility of using the known metabolic precursors of the sialic acids, particularly N-acetyl-[6-3H]mannosamine, to label and identify various forms of sialic acids in tissue culture cells. Firstly, we defined several variables that affect the labeling of sialic acids with N-acetyl-[6-3H]mannosamine. Secondly, we have devised a simple screening method to identify cell lines that synthesize substituted or modified sialic acids. We next demonstrate that it is possible to definitively identify the natures of the various labeled sialic acids without the use of mass spectrometry, even though they are present only in tracer amounts. The methods used include paper chromatography, analytical de-O-acetylation, periodate release of the 9-3H as [3H]formaldehyde (which is subsequently converted to a specific 3H-labeled chromophore), acylneuraminate pyruvate lyase treatment with identification of [3H]acylmannosamines, gas-liquid chromatography with radioactive detection, and two new high-pressure liquid chromatography methods utilizing the amine-adsorption:ion suppression and ion-pair principles. The use of an internal N-acetyl-[4-14C]neuraminic acid standard in each of these methods assures precision and accuracy. The combined use of these methods now allows the identification of radioactive tracer amounts of the various types of sialic acids in well-defined populations of tissue culture cells; it may also allow the identification of hitherto unknown forms of sialic acids.

Determination of 3-deoxy-D-manno-octulosonic acid (KDO), N-acetylneuraminic acid, and their derivatives by ion-exchange liquid chromatography

A liquid chromatography (1.6 MPa) system for the analysis of 3-deoxy-D-manno-2-octulosonic acid (KDO), N-acetylneuraminic acid (Neu5Ac), methyl alpha- and beta-glycosides of Neu5Ac and KDO, alpha-heptosyl-(1----5)-KDO, various sialyllactoses, alpha-KDO-(2----4)-KDO, alpha-KDO-(2----4)-KDO methyl alpha-glycoside, beta-KDO-(2----4)-KDO methyl beta-glycoside, D-glucuronic acid, D-glucurono-3,6-lactone, and D-galacturonic acid has been developed. Separation was achieved within 10 and 30 min by the use of a small column filled with a strongly basic, anion-exchange resin, Aminex A-29, and 0.75 or 10mM sodium sulfate solutions as mobile phases. This method allowed the determination of KDO and sialic acids in amounts of 100 ng (0.5 nmol) and 200 pg (0.6 pmol), respectively.

Structural analysis of underivatized sialic acids by combined high-performance liquid chromatography-mass spectrometry

Mass spectra of chemically ionized, positive ions of underivatized N,O-acylated sialic acids, 2-deoxy-2,3-didehydro-N-acetylneuraminic acid and sialyl-alpha(2-3)-lactose were obtained by combined high-performance liquid chromatography--mass spectrometry, using a direct liquid inlet system. The mass spectra of the different compounds for which fragmentation schemes are proposed enable the differentiation between sialic acids, although the localization of O-substituents is not possible. However, since the various sialic acids separated well on high-performance liquid chromatography, combined high-performance liquid chromatography-mass spectrometry allowed their unequivocal characterization.

Automatic amino acid and sugar analysis of glycoproteins

Amino acid analyzers were used for complete analyses of glycoproteins. The methods of analysis used were cation-exchange chromatography for amino acids, phosphoamino acids and amino sugars with ninhydrin as reagent, and anion-exchange chromatography for neutral sugars with copper Bicinchoninate as reagent. A separate program was developed for the analysis of charged sugar components, N-acetylneuraminic acid and amino sugars in one chromatogram. The possibility of detection of radioactively labelled components is also demonstrated. The detection limits and possibilities for column and reactor switches are discussed.

Identification of a disialoganglioside (GD1a) containing terminal N-acetyl-9-O-acetylneuraminic acid in rat erythrocytes

Gangliosides containing 350 micrograms of sialic acids were isolated from 2.85 X 10(11) rat erythrocytes and found to be mainly composed of GD1a and an unknown alkali-labile species which was converted to GD1a after treatment with ammonia. Smaller amounts of GM1 and Fuc-GM1 were also present. Identification of the sialic acids of the novel species by thin-layer chromatography, high performance liquid chromatography and gas-liquid chromatography--mass spectrometry revealed the presence of both N-acetylneuraminic acid and N-acetyl-9-O-acetyl-neuraminic acid in about equimolar amounts. Incubation of the isolated ganglioside with Vibrio cholerae sialidase released N-acetyl-9-O-acetyl-neuraminic acid. Non O-acetylated GM1 was identified as the only remaining ganglioside by thin-layer chromatography. Thus this novel ganglioside has the following structure: Neu5,9Ac2 alpha 2-3Gal beta 1-3GalNAc beta 1-4(Neu5Ac alpha-2-3)Gal beta 1-4Glc beta 1-1'Cer.

Malaria parasites do not contain or synthesize sialic acids

The capacity of Plasmodia to synthesize sialic acids was investigated by adding radioactive acetate to short-term in vitro cultures of the intraerythrocytic asexual forms of three malaria parasites (the human malaria Plasmodium falciparum in Aotus trivirgatus erythrocytes; the simian malaria P. knowlesi in rhesus monkey erythrocytes; the rodent malaria P. berghei in mouse erythrocytes) and to cultures of extracellular zygotes of the avian malaria P. gallinaceum. Radioactive acetate was added to normal rhesus monkey erythrocytes and to cells of the murine myeloma NS-1 for comparison. Although [1-14C]-acetate labeled many proteins with each malaria parasite and the NS-1 cells, analysis of purified sialic acids revealed that only with the NS-1 cells was radioactivity incorporated into sialic acids. Furthermore, N-acetyl[6-3H]mannosamine was not incorporated into sialic acids or malarial glycoproteins when added to P. knowlesi cultures. All of the malaria parasites underwent growth or differentiation during these experiments as measured by [35S]methionine uptake into protein and by light microscopy. Extracellular parasites largely free of erythrocyte membranes were prepared to determine whether Plasmodia contain sialic acids that are not labeled by exogenous precursors. Purified merozoites of P. knowlesi and zygotes of P. gallinaceum did not contain detectable amounts of sialic acids on chemical analysis. Thus, although we could show that Plasmodia can incorporate radioactive sugars such as glucosamine, galactose and mannose into proteins, presumably glycoproteins, they do not synthesize sialic acids or sialo-glycoproteins, nor do they contain sialo-glycoconjugates of host origin.