Figure 3.

Identification of a phosphorylation site on α-Casein-S2 by hierarchical MS²/MS³ database search. The figure demonstrates the capability of hierarchical search to localize the phosphorylation on a phosphopeptide containing multiple possible phosphorylation sites. The MS² (top) and MS³ (bottom) spectra are shown to highlight the effect of neutral loss on the MS² spectra. The detected phosphorylation site was previously reported by Kweon and Hakansson [10]. Neutral losses in the figure are labeled as follows: ^~ (loss of phosphate moiety),* (loss of ammonia), ' (loss of water).