Fig. 3.

A histogram of the ratios of iTRAQ-labels of phosphopeptides derived from cytosolic proteins of Xenopus eggs without and with a Ca²⁺-stimulus. Phosphopeptides in tryptic digests of cytosol fractions (3 mg protein) of Xenopus eggs without and with a Ca²⁺-stimulus were purified with an automated phosphopeptide purification system with 1-step elution method, and then modified with 114- and 117-iTRAQ, respectively. The thus labelled phosphopeptides were mixed, desalted and dissolved in the EDTA-containing solvent. The labelled phosphopeptides derived from 1.6 mg protein were analysed three times by LC MS/MS, and the 117/114 ratios were determined. The histogram was made using 112 phosphopeptides reproducibly detected three times.