Fig. 8: Schematic diagram of the proposed PSI electron pumping cycle.
From: Structure of cyanobacterial photosystem I complexed with ferredoxin at 1.97 Å resolution
a Reduced Cyt c6 and oxidized Fd are in a free unbound state. b Light-induced charge separation across the membrane causes oxidized Fd to bind on the stromal side and opens up non-productive docking sites for Cyt c6 on the luminal side. The pink heart-shaped symbol represents an activated binding site and the ‘closed’ traffic sign represents a closed reaction center. c Cyt c6 is bound to luminal non-productive docking sites while permanently oxidized Ga-Fd remains bound at the stromal side with the dashed line frame indicating the structure determined in this study. d The excited electron has left PSI with its soluble carrier Fd and the reduced Cyt c6 has moved to the productive P700* proximal binding site for electron transfer and subsequent detachment from PSI.
