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  • Title: Spin-lattice relaxation of the phyllosemiquinone radical of photosystem I.
    Author: Deligiannakis Y, Hanley J, Rutherford AW.
    Journal: Biochemistry; 1998 Mar 10; 37(10):3329-36. PubMed ID: 9521653.
    Abstract:
    The spin-lattice relaxation time (T1) of the phyllosemiquinone anion radical, A1-, of the photosystem I (PSI) reaction center, were measured between 4.5 and 85 K by electron spin-echo spectroscopy. The selective removal of the iron-sulfur centers, FA, FB, and FX, from PSI allowed the measurement of the intrinsic T1 of the A1- radical. The temperature dependence of the intrinsic (T1)-1 for A1- was found to be approximately T1.3 +/- 0.1. The spin-lattice relaxation of the reduced form of iron-sulfur center FX was also measured at low temperatures, in FA/FB-depleted PSI membranes. It was found that the fast-relaxing FX center enhances the spin-lattice relaxation of the phyllosemiquinone due to dipolar coupling. The effect of the reduced forms of FA/FB on the T1 of the phyllosemiquinone was minor compared to the effect of FX. By analyzing the data with a dipolar model in the light of limitations imposed by other information present in the literature, the distance between the phyllosemiquinone and FX in PSI is estimated to be 14.8 +/- 4 A.
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