Figure 2. Quantitative identification of IDPs and oxidized IDPs in mouse tissues. A, LC-ESI-MS/MS analysis of endogenous carnosine in the mouse skeletal muscle. Representative LC-ESI-MS/MS chromatograms of spiked isotope-labeled carnosine (upper trace), and endogenous carnosine (lower trace) are shown. B, LC-ESI-MS/MS analysis of endogenous 2-oxo-carnosine in the mouse skeletal muscle. Representative LC-ESI-MS/MS chromatograms of spiked isotopelabeled 2-oxo-carnosine (upper trace), and endogenous 2-oxo-carnosine (lower trace) are shown. C, quantitative identification of IDPs (upper graph) and oxidized IDPs (lower graph) in the mouse tissues. The IDPs and oxidized IDPs in mouse tissues were quantified using LC-ESI-MS/MS coupled with a stable isotope dilution method. The data are means Ϯ S.D. (n ϭ 3). 2-Oxo-IDPs are functional oxidation products

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