Time-resolved X-, K-, and W-band EPR of the radical pair state P{sub 700}{sup {center_dot}-}A{sub 1}{sup {center_dot}-} of photosystem I in comparison with P{sub 865}{sup {center_dot}+}Q{sub A}{sup {center_dot}-} in bacterial reaction centers
- Freie Universitaet, Berlin (Germany)
- Technische Universitaet Berlin (Germany)
The spin-polarized EPR spectra at 95 GHz (W-band), 24 GHz (K-band), and 9 GHz (X-band) of the radical pair P{sub 700}{sup {center_dot}+}A{sub 1}{sup {center_dot}-} in highly purified photosystem I particles are presented. The spectra are analyzed to obtain both the magnetic parameters of the radical pair as well as the relative orientation of the two species. From the analysis, the g-tensor of A{sub 1}{sup {center_dot}-} is found to be g{sub xx} = 2.0062, g{sub yy} = 2.0051, and g{sub zz} = 2.0022, and it is shown that A{sub 1} is oriented such that the carbonyl bonds are parallel to the vector joining the centers of P{sub 700}{sup {center_dot}+} and A{sub 1}{sup {center_dot}-}. The anisotropy of the g-tensor is considerably larger than that obtained for chemically reduced phylloquinone in frozen 2-propanol solution. Possible reasons for this difference and their implications for the A{sub 1} binding site are discussed. The relative orientation of P{sub 700}{sup {center_dot}+} and A{sub 1}{sup {center_dot}-} is compared with earlier estimates obtained using less accurate g-values for A{sub 1}{sup {center_dot}-}. A comparison with the spectra of P{sub 865}{sup {center_dot}+}Q{sub A}{sup {center_dot}-} in bacterial reaction centers (bRCs) of Rhodobacter sphaeroides R-26 in which the nonheme iron has been replaced by zinc (Zn-bRCs) allows the structural and magnetic properties of the charge-separated state in the two systems to be compared. 52 refs., 5 figs., 7 tabs.
- OSTI ID:
- 502024
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 101, Issue 8; Other Information: PBD: 20 Feb 1997
- Country of Publication:
- United States
- Language:
- English
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