Stable isotope labeling of aminosugars with ¹⁵N/¹³C-glucosamine

Stable isotope labeling is an effective method for introducing a “marker” into a molecule of interest.  Glycans labeled with stable isotopes are useful in many scientific fields such as detection of diagnostic markers, analyses of metabolic fluxes and even structural analyses of glycans or glycoproteins by mass spectrometry or NMR.  Labeling methods are generally classified into two categories, namely, in vitro labeling and metabolic labeling.  In vitro labeling introduces labeled sugars, typically enzymatically, into purified glycans or glycoproteins,  For example, galactosyltransferase or sialyltransferase transfers labeled sugar nucleotides, such as UDP-[¹³C]Gal or CMP-[¹³C]Sia, onto the non-reducing glycan termini ^{1) 2)}.  Metabolic labeling is typically performed by cultivating cells in a medium which includes the labeled metabolic precursor.  Glucose is generally used for labeling sugar residues (GlcNAc, Man, Fuc, Gal, Sia, etc) while glucosamine is rather specifically incorporated into GlcNAc, GalNAc and Sia residues (Fig. 1).  Here we introduce a method for metabolic labeling of amino sugar residues (GlcNAc) on IgG-Fc glycans using labeled glucosamine ^{2) 3) 4)}.

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