Fig. 3.

Sequencing of a phosphopeptide released, by proteolysis with trypsin and chymotrypsin, from PSI complexes isolated from psae1-3 leaves. a Fragmentation spectrum (MS2) of the doubly protonated and phosphorylated peptide from psae1-3. b MS2 spectrum of the synthesized phosphorylated peptide tGSLAGDNGFDPLGLAEDPENLK. c MS2 spectrum of the synthesized non-phosphorylated peptide TGSLAGDNGFDPLGLAEDPENLK. Note that no neutral loss of H₃PO₄ (NL; m/z = −49) is observed. The b- and y-ions are indicated in the spectra and in the corresponding peptide sequence. The peptide fragment that underwent neutral loss of H₃PO₄ is indicated as NL. The lowercase t designates pThr