Fig. 1: Comparison of electron transfer chains in PSI.
From: Structure of the far-red light utilizing photosystem I of Acaryochloris marina
a Cyanobacterial and higher plant PSI. b A. marina PSI identified in this work. In cyanobacterial and higher plant PSI, electrons released from the paired Chls, so-called special pair, of P700, a heterodimer of Chl a and a′, are transferred to ferredoxin (Fd) to reduce NADP+ via Acc (Chl a), A0 (Chl a), A1 (PhyQ), FX (iron–sulfur center), and FA/FB (iron–sulfur center). The components are arranged in a pseudo-C2 axis on a heterodimer reaction center protein complex (PsaA/PsaB) and the two routes (A- and B-branch located on PsaA and PsaB, respectively) are thought to be equivalent. Acc accessory chlorophyll, A0 primary electron acceptor, A1 secondary electron acceptor, FX, FA, and FB iron–sulfur centers, PhyQ phylloquinone. In A. marina PSI, the electron transfer chain is the same, but some cofactors differ from those in the PSIs of other organisms; the Chls of special pair P740 are Chl d/d′, while Acc could be Chl d (see text for detail) and A0 is pheophytin (Pheo) a.
