This Article Full Text Full Text (PDF) Supplement All Versions of this Article: biophysj.107.122242v1 94/12/4783    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Di Donato, M. Articles by Groot, M. L. PubMed PubMed Citation Articles by Di Donato, M. Articles by Groot, M. L.

Primary Charge Separation in the Photosystem II Core from Synechocystis: A Comparison of Femtosecond Visible/Midinfrared Pump-Probe Spectra of Wild-Type and Two P₆₈₀ Mutants

Mariangela Di Donato ^*, Rachel O. Cohen , Bruce A. Diner , Jacques Breton , Rienk van Grondelle ^* and Marie Louise Groot ^*

^* Department of Physics, Free University Amsterdam, Amsterdam, The Netherlands; Central Research and Development, Experimental Station, E. I. du Pont de Nemours, Wilmington, Delaware; and Commisariat à l'Énergie Atomiqiue Saclay, Gif-sur Yvette, France

Correspondence: Address reprint requests to Rienk van Grondelle, E-mail: rienk{at}nat.vu.nl.

It is now quite well accepted that charge separation in PS2 reaction centers starts predominantly from the accessory chlorophyll B_A and not from the special pair P₆₈₀. To identify spectral signatures of B_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_B (D2-His¹⁹⁷) has been changed to Ala or Gln. By analogy with the structure of purple bacterial reaction centers, the mutated histidine is proposed to be indirectly H-bonded to the C₉=O carbonyl of the putative primary donor B_A through a water molecule. The constructed mutations are thus expected to perturb the vibrational properties of B_A by modifying the hydrogen bond strength, possibly by displacing the H-bonded water molecule, and to modify the electronic properties and the charge localization of the oxidized donor Analysis of steady-state light-induced Fourier transform infrared difference spectra of the WT and the D2-His¹⁹⁷Ala mutant indeed shows that a modification of the axially coordinating ligand to P_B induces a charge redistribution of In addition, a comparison of the time-resolved visible/midinfrared spectra of the WT and mutants has allowed us to investigate the changes in the kinetics of primary charge separation induced by the mutations and to propose a band assignment identifying the characteristic vibrations of B_A.