Fig. 1.

Spatial arrangement of cofactors in PS2. Schematic structure of the PSII core complex of Thermosynechococcus elongatus (3) obtained with the program PYMOL (DeLano Scientific, South San Francisco, CA) is shown. On the donor side, two Chls (P_D1 and P_D2) and two accessory Chls (Chl_D1 and Chl_D2) are localized. At the acceptor side, two Phe cofactors and two quinones are localized. The cofactors are nearly arranged in a C₂ symmetry perpendicular to the membrane plane as indicated by the axis.