Primary Charge Separation in the Photosystem II Core from Synechocystis: A Comparison of Femtosecond Visible/Midinfrared Pump-Probe Spectra of Wild-Type and Two P^sub 680^ Mutants

ABSTRACT

It is now quite well accepted that charge separation in PS2 reaction centers starts predominantly from the accessory chlorophyll B^sub A^ and not from the special pair P^sub 680^. To identify spectral signatures of B^sub A^, and to further clarify the process of primary charge separation, we compared the femtosecond-infrared pump-probe spectra of the wild-type (WT) PS2 core complex from the cyanobacterium Synechocystis sp. PCC 6803 with those of two mutants in which the histidine residue axially coordinated to P^sub B^ (D2-His^sup 197^) has been changed to Ala or Gln. By analogy with the structure of purple bacterial reaction centers, the mutated histidine is proposed to …