Pulsed EPR study of spin-coupled radical pairs in photosynthetic reaction centers: Measurement of the distance between P{sub 700}{sup {center_dot}+} and A{sub 1}{sup {center_dot}-} in photosystem I and between P{sub 865}{sup {center_dot}+} and Q{sub A}{sup {center_dot}-} in bacterial reaction centers
- Technische Universitaet Berlin (Germany)
The spin-polarized radical pairs P{sub 865}{sup {center_dot}+}Q{sub A}{sup {center_dot}-} in protonated and deuterated Zn-substituted reaction centers from two different mutants of the photosynthetic bacteria Rhodobacter sphaeroides and P{sub 700}{sup {center_dot}+}A{sub 1}{sup {center_dot}-} in plant photosystem I from Synechococcus elongatus are investigated by pulsed EPR spectroscopy. Spin-polarized radical pairs give rise to a characteristic out-of-phase electron spin echo. This echo shows a deep envelope modulation with a frequency governed by the spin-spin interaction. The known distance dependence of the magnetic dipolar interaction allows the determination of the distance between the cofactors carrying the unpaired electron spins. For the bacterial reaction centers this distance is known for the electronic ground state from crystal structures and is compared here with the distance of the radical pair spins, i.e. the charge-separated state. In photosystem I the location of the acceptor A{sub 1} is not known yet. A distance of 25.4 {+-} 0.3 angstrom between P{sub 700}{sup {center_dot}+} and A{sub 1}{sup {center_dot}-} is obtained here and gives new structural information on photosystem I. 42 refs., 6 figs.
- OSTI ID:
- 502025
- 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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