In this work we investigated the role of plastocyanin (PC) phosphorylation in photosynthetic electron transfer, focusing on PC's interaction with both cytochrome b6f, (Cytb6f) and photosystem I (PSI) in Chlamydomonas reinhardtii. While the binding and electron transfer between PC and PSI are well characterized, the interaction between PC and Cytf remains less clear. Using chemical crosslinking combined with mass spectrometry, we identified two potential binding models for PC and Cytf: Side-on and Head-on.