High-performance liquid chromatography of reducing carbohydrates as strongly ultraviolet-absorbing and electrochemically sensitive 1-phenyl-3-methyl-5-pyrazolone derivatives

The unique N-terminal sequence of testis angiotensin-converting enzyme is heavily O-glycosylated and unessential for activity or stability

The testis-specific isozyme of angiotensin-converting enzyme (ACE) is identical, from residue 68 to the C terminus, to the second half or C-terminal domain of somatic ACE. However, the first 67 residues, comprising the signal peptide and a Ser-/Thr-rich 36-residue sequence that constitutes the N terminus of mature testis ACE, are unique. We have expressed a mutant human testis ACE lacking this 36-residue N-terminal sequence and find that compared to the wild-type protein the mutant is 15 kDa smaller due to the loss of greater than 90% of all O-linked sugars, but that it retains full enzymatic activity and is stable in culture. Heavy O-glycosylation is a property of testis ACE that is not shared by the somatic enzyme and is attributable to this unique sequence.

Precolumn labeling of reducing carbohydrates with 1-(p-methoxy)phenyl-3-methyl-5-pyrazolone: analysis of neutral and sialic acid-containing oligosaccharides found in glycoproteins

A convenient precolumn labeling method was developed for the analysis of neutral and sialic acid-containing oligosaccharides in glycoproteins using 1-(p-methoxy)phenyl-3-methyl-5-pyrazolone (PMPMP). PMPMP reacts with a reducing oligosaccharide under slightly alkaline conditions (pH 8.3) to form a 2:1 adduct (bis-PMPMP derivative). Sialic acid residues in the oligosaccharides remain intact during the reaction. Tryptic glycopeptides digested with glycopeptidase A for oligosaccharide liberation can be directly derivatized with PMPMP without prior treatment. Separation of the labeled oligosaccharides was performed by reverse-phase high-performance liquid chromatography on a C-18 column with aqueous acetonitrile, and positional isomers such as isomeric triantennary tetradecasaccharides from bovine fetuin were completely resolved. The bis-PMPMP derivatives were labile in alkaline media to form mono-PMPMP derivatives; however, the mono-PMPMP derivatives could be easily reconverted to the original bis-PMPMP derivatives. The proposed method is simpler than the reductive pyridylamination method, and detection sensitivity could reach subnanomole range with a uv detector. Oligosaccharides from ribonuclease B (bovine pancreas), ovalbumin, thyroglobulin (porcine thyroid), fetuin (bovine), and transferrin (human) have been successfully analyzed to demonstrate the usefulness of this method as an alternative to the existing methods.

Quantitative determination of phenyl isothiocyanate-derivatized amino sugars and amino sugar alcohols by high-performance liquid chromatography

Simple and rapid methods for the preparation of phenylthiocarbamyl (PTC) derivatives of amino sugars and amino sugar alcohols and their quantitative determination with high sensitivity (less than 10 pmol) by C18 reversed-phase high-performance liquid chromatography are described. Rapid sample preparation of the phenyl isothiocyanate (PITC)-derivatized amino sugars and amino sugar alcohols was achieved by a simple extraction of the reaction mixture with chloroform to remove the excess PITC and its adducts. Baseline separation of the PTC derivatives of amino sugars and amino sugar alcohols was obtained within 30 min, using a simple solvent system consisting of 0.2% each of n-butylamine, phosphoric acid, and tetrahydrofuran. The mobile phase containing n-butylamine, in conjunction with a C18 stationary phase, mimics the conditions for the separation of carbohydrates on an amino-bonded column. GlcNH2 and GalNH2 derived from the initial protein-sugar linkages were also separated from the amino acids for quantitative estimation of sugar chains in glycoproteins. Amino sugar alcohols gave single reaction products with PITC while the reaction with amino sugars was accompanied by the formation of secondary products. Apparently the secondary products were formed in an acid-catalyzed intramolecular cyclization of the PTC-hexosamines involving the aldehyde functional group. Conditions were developed to stop the transformations and maintain the stability of PTC derivatives for their convenient determination by HPLC.

A reversed-phase ion-pair high-performance liquid chromatography method for bovine testicular hyaluronidase digests using postcolumn derivatization with 2-cyanoacetamide and ultraviolet detection

A reversed-phase ion-pair HPLC method for separating hyaluronic acid oligomers, using a polymeric C18 column at alkaline pH, is described. As the concentration of the ion-pairing agent tetrabutylammonium hydroxide increased, over the range of 0.01 to 0.06M, the capacity factors (k') of tetra- to dodecasaccharide decreased. The change in k', for each increment in pairing agent, increased with oligomer molecular weight. When changing mobile phase pH from 7 to 8, k' dramatically decreased and remained unchanged from pH 8 to 11. The isocratic separation was optimized to resolve tetrato dodecasaccharide at pH 9.0 in under 19 min. The postcolumn derivatizing agent 2-cyanoacetamide reacted with the reducing N-acetylglucosamine end groups of hyaluronic acid oligomers to yield reaction products that were monitored at 27 nm. In a series of control experiments using decasaccharide and N-acetylglucosamine, it was found that maximum product formation took place at pH 9 and was greatly influenced by borate buffer concentration. The optimum concentration for 2-cyanoacetamide was 0.33% and a temperature of 100 degrees C gave the best signal to noise ratio for the postcolumn reaction. The method is linear and reproducible, and has a lower limit of detection for tetrasaccharide of 20 ng (25 pmol). This system is suitable for studying the degradation kinetics of purified hyaluronic acid oligomers by bovine testicular hyaluronidase. Extension of the method to fluorescent and electrochemical detection and its applicability to other glycosaminoglycans is discussed.

Synthesis and application of Fmoc-hydrazine for the quantitative determination of saccharides by reversed-phase high-performance liquid chromatography in the low and subpicomole range

A new derivatization reagent, Fmoc-hydrazine, has been synthesized from the reaction of Fmoc-chloroformate with hydrazine as a precolumn fluorometric labeling reagent for reducing sugars such as glucose, galactose, mannose, fructose, fucose, ribose, xylose, arabinose, lactose, and maltose. The optimization of derivatization conditions was examined in detail. Using a reversed-phase high-performance C-8 column and a mobile phase consisting of acetonitrile-aqueous acetic acid, seven sugar derivatives were separated under either isocratic or gradient conditions within 20 min. The Fmoc-hydrazine and sugar Fmoc-hydrazone derivatives exhibit excellent stability. The extent of the hydrazone formation was 77 and 82% for mannose and fucose as assessed by Dionex high-performance anion-exchange chromatography with pulsed amperometric detection. Linear calibration graphs were established in the range from 0.5 to 2 pmol and 12 to 110 pmol for individual sugar derivatives. The determination limits were 0.05-0.09 pmol for mannose, galactose, and ribose; 0.1 pmol for maltose, xylose, and glucose; 0.2 pmol for fucose and lactose; 0.3 pmol for arabinose; and 0.4 pmol for fructose. The component monosaccharides of ultramicroquantities of two glycoproteins (e.g., from 7 ng fetuin and ovalbumin) were determined in the subpicomole range.

Ultrasensitive fluorometric detection of carbohydrates as derivatives in mixtures separated by capillary electrophoresis

Reducing monosaccharides and oligosaccharides, after reductive amination, were separated and detected as their 3-(4-carboxybenzoyl)-2-quinolinecarboxaldehyde (CBQCA) derivatives by capillary electrophoresis/laser-induced fluorescence. Under optimized conditions, the minimum detectable quantities for monosaccharide solutes were assessed at low attomole levels (0.5 amol for the CBQCA derivative of galactose). The system has shown considerable promise for high-sensitivity analysis of both neutral and amino sugars in glycoproteins. Complex oligosaccharides, isolated from bovine fetuin by hydrazinolysis, were also successfully "mapped."