Separation of oligosaccharides by capillary supercritical fluid chromatography and analysis by direct coupling to high-resolution mass spectrometer: application to analysis of oligomannosidic N-glycans

Use of compounds naturally labeled with stable isotopes for the study of the metabolism of glycoprotein neutral sugars by gas-liquid chromatography-isotope-ratio mass spectrometry. Technical validation in the rat

In order to develop an alternative method to radioactive labeling for the study of the glycoprotein sugar metabolism in man, the possible use of stable isotopes provided by naturally, 13C-enriched dietary compounds has been explored in rat intestine and serum. Rats were fed a semisynthetic diet containing 67% wheat starch (containing 1.08692 13C atom/100 carbon atoms) for a week, and then the same diet containing corn starch (1.10042% 13C) for a week. Neutral sugars were prepared from delipidated, trichloroacetic acid-precipitable material from 200-400 mg of intestinal mucosa or 1 mL of serum, separated, and analyzed as alditol acetates by gas-liquid chromatography coupled to isotope-ratio mass spectrometry. This technique allowed the determination, in a single experiment, of the amount and 13C abundance of six neutral sugars (including xylose used as internal standard). Despite the low abundance of 13C in natural products, the sensitivity of the technique was found to be sufficient to detect isotopic enrichment as low as 0.001% with good accuracy and reproducibility in 2 micrograms of each glycoprotein neutral sugar. As an example, the pattern of labeling by dietary D-glucose from corn starch appears to be very different for fucose, ribose, mannose, galactose, and glucose of intestine or serum macromolecules.

Carbohydrate analysis

The analysis of the carbohydrate chains attached to proteins is becoming increasingly important as appreciation of the role of glycosylation in the structural and functional properties of biologically significant glycoproteins grows. Over the past year, a number of developments have been made that may improve and promote the analysis of the glycosylation of proteins.

Characterization of a novel type of chain-terminator Gal beta 1-6Gal beta 1-4)GlcNAc in an oligosaccharide related to N-glycosylated protein glycans isolated from GM1 the urine of patients with gangliosidosis

Two new oligosaccharides were isolated from the urine of a patient with GM1 gangliosidosis. Final purification of the oligosaccharides was accomplished by capillary supercritical fluid chromatography. Structural analysis was by chemical analysis, chemical-ionization mass spectrometry and 400-MHz 1H-NMR spectroscopy, leading to two primary structures. The first is derived from a classical triantennary N-acetyllactosamine-type glycan: Gal beta 1-4GlcNAc beta 1-4(Gal beta 1-4GlcNAc beta 1-2)Man alpha 1-3Man beta 1-4GlcNAc. The second is unusual with a terminal disaccharide Gal beta 1-6Gal, which had not yet been described for glycans of the N-acetyllactosamine type: Gal beta 1-6Gal beta 1-4GlcNAc beta 1-2Man alpha 1-6Man beta 1-4GlcNAc.

Characterization of N-linked glycans by supercritical fluid chromatography-mass spectrometry

N-Linked glycans have been characterized by supercritical fluid chromatography (SFC) and SFC-MS using positive- and negative-ion chemical ionization. Four common oligosaccharide derivatives have been prepared and their chromatographic properties assessed on three SFC columns of varying polarity. Carbon dioxide has been used as the SFC mobile phase, with ammonia or CO2 added to the ion source for positive- and negative-ion chemical ionization, respectively. Direct SFC-MS interfacing allows the analytical manipulations of single-ion monitoring, total-ion plots, background subtraction, library searches, and spectral reconstruction algorithms. Positive ammonia chemical ionization yields abundant molecular-weight information, (MH)+, and (MNH4)+ with little or no fragmentation. To capitalize on sensitivity, samples were prepared with the pentafluorobenzyl aminobenzoate reagent, acetylated, and analyzed by SFC-NICI-MS. This modification improves column efficiency and resolution and greatly enhances detecting sensitivity. These "soft" ionization conditions provide abundant molecular-weight-related anions for collision-induced dissociation and subpicogram detection.