Excited states of the 5-chlorophyll photosystem II reaction center

Journal Article · Thu Nov 04 04:00:00 EST 1999 · Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical

DOI:https://doi.org/10.1021/jp9906738· OSTI ID:20003205

Jankowiak, R; Raetsep, M; Picorel, R; Seibert, M; Small, G J

Results of 4.2 K hole burning, chemical reduction (sodium dithionite, in dark and with illumination), and oxidation (ferricyanide) experiments are reported for the isolated PS II reaction center containing five chlorophyll (Chl) molecules (RC-5). Q{sub y} states at 679.6 and 668.3 nm are identified as being highly localized on pheophytin a of the D{sub 1} branch (Pheo{sub 1}) and pheophytin a of the D{sub 2} branch (Pheo{sub 2}), respectively. The Pheo{sub 1}-Q{sub x} and Pheo{sub 2}-Q{sub x} transitions were found to lie on the low and high energy sides of the single Pheo-Q{sub x} absorption band, at 544.4 and 541.2 nm, respectively. The Q{sub y} band of the 684 nm absorbing Chl, which is more apparent in absorption in RC-5 than in RC-6 samples, is assigned to the peripheral Chl on the D{sub 1} side. The results are consistent with that peripheral Chl being Chl{sub z}. The results indicate that P680, the primary electron donor, is the main acceptor for energy transfer from the Pheo{sub 1}-Q{sub y} state and that excitation energy transfer from the Pheo{sub 1}-Q{sub y} state and P680* to the 684 nm Chl is inefficient. It is concluded that the procedure used to prepare RC-5 has only a small effect on the energies of the Q{sub y} states associated with the core cofactors of the 6-Chl RC as well as the 684 nm Chl. Implications of the results for the multimer model are considered. In that model the Q{sub y}-states of the core are significantly delocalized over several cofactors. The results presented provide no support for this model.

• Research Organization: Ames Lab., IA (US)
• Sponsoring Organization: US Department of Energy
• DOE Contract Number: W-7405-ENG-82; AC36-99GO10337
• OSTI ID: 20003205
• Journal Information: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical Journal Issue: 44 Vol. 103; ISSN JPCBFK
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
CHLOROPHYLL
ELECTRONIC STRUCTURE
EXCITED STATES
PHOTOSYNTHETIC REACTION CENTERS
REDUCTION