Figure 1 - Accurate quantification of known O-GlcNAc peptides from complex mixtures using the QUIC-Tag approach.
From the following article
Probing the dynamics of O-GlcNAc glycosylation in the brain using quantitative proteomics
Nelly Khidekel, Scott B Ficarro, Peter M Clark, Marian C Bryan, Danielle L Swaney, Jessica E Rexach, Yi E Sun, Joshua J Coon, Eric C Peters & Linda C Hsieh-Wilson
Nature Chemical Biology 3, 339 - 348 (2007) Published online: 13 May 2007
doi:10.1038/nchembio881
(a) Extracted ion chromatograms of the heavy and light forms of two representative O-GlcNAc-glycosylated peptides, 
-crystallin peptide 158-AIPVSREEKPSSAPSS-173 (top) and OGT peptide 390-ISPTFADAYSNMGNTLK-406 (bottom). Co-elution by reverse-phase liquid chromatography was observed. (b) Quantification from the isotopic cluster of the heavy (m/z = 810.061) and light (m/z = 806.416) forms of the -crystallin peptide yielded a heavy:light ratio of 0.97 -
0.09, 0.97 + 0.10 (g.s.d. = 1.10). Quantification of the heavy (m/z = 1,308.605) and light (m/z = 1,302.569) forms of the OGT peptide yielded a heavy:light ratio of 0.93 -
0.12, 0.93 + 0.14 (g.s.d. = 1.15). Before labeling, both proteins were added to neuronal lysates at a ratio of 1:1 (n = 7).
