Figure 3.

Scheme of a multiplex reaction of 4 different samples, designated by 4 different colors. A) Four samples (2 controls, CON1 and CON2, and 2 AD, AD1 and AD2) of brain lysates (100 μg; each labeled with different colors) were subjected to proteolytic digestion by trypsin followed by SPE clean up. Digested peptides were labeled in each sample by iTRAQ reagents [control 1 (red), 114.11; control 2 (blue), 115.11; AD1 (green), 116.11; and AD2 (orange), 117.11]. All the samples were processed in parallel. Labeled samples were combined, and phosphopeptides are enriched by TiO₂ chromatography and analyzed by LC/MS/MS. B) MS/MS spectra of one of the phosphopeptides. C) iTRAQ reporter ion region of the MS/MS spectrum.