Selective analysis of intracellular UDP-GlcNAc and UDP-GalNAc by hydrophilic interaction liquid chromatography-mass spectrometry.

Uridine diphosphate--acetylglucosamine (UDP-GlcNAc) is one of the major nucleotide sugars in living organisms and serves as the key donor substrate for the post-translational modification of protein -GlcNAcylation. It undergoes interconversion to its epimer uridine diphosphate--acetylgalactosamine (UDP-GalNAc), which acts as a sugar donor initiating mucin-type -linked glycosylation. The intracellular levels of the two differ between the cell lines and largely fluctuate in response to metabolic perturbations, and recent studies have focused on the details of their biosynthesis or turnover. However, due to their similar chemical properties, sufficient resolution for the two epimers required non-volatile mobile phases that cannot be applied directly to a mass spectrometer. In this study, to implement simple liquid chromatography-mass spectrometry for UDP-GlcNAc and UDP-GalNAc, we optimized a condition of hydrophilic interaction liquid chromatography-mass spectrometry. We found that the use of ammonium hydroxide and an amide column with an optimized water-acetonitrile ratio, flow rate, and column temperature, provided complete separation of the two. The method allowed the analysis of intracellular levels, a stable isotope-labeled target, and patterns of product ion spectra in a single run with fewer sample preparation steps. The new method can be widely used for mass spectrometric analysis of UDP-GlcNAc and UDP-GalNAc.