Identification and relative quantitation of detected phosphopeptides. (Top) Extracted ion chromatograms (XICs) of monoisotopic peaks were used to calculate peptide ratios (blue indicates control sample; purple, 10 minutes of PGE2 [10μM]; green, 60 minutes of PGE2 [10μM]). (Bottom) Tandem mass spectrometry spectra of detected phosphopeptides. (A) Phosphopeptide from AP-3 complex subunit δ-1 protein with phosphorylation at Ser567. (B) Phosphopeptide from Histone H1.4 protein with phosphorylation at Ser35. For complete mass spectrometry results, please refer to supplemental Table 4 and supplemental data.