Delayed fluorescence from the photosynthetic reaction center measured by electronic gating of the photomultiplier |
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Authors: | Filus Z Laczkó G Wraight C A Maróti P |
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Affiliation: | Department of Biophysics, University of Szeged, P.O.Box 655, Szeged, Hungary. |
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Abstract: | The decay of the delayed fluorescence (920 nm) of reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides R26 in the P(+)Q(A)(-) charge-separated state (P and Q(A) are the primary donor and quinone, respectively) has been monitored in a wide (100 ns to 100 ms) time range. The photomultiplier (Hamamatsu R3310-03) was protected from the intense prompt fluorescence by application of gating potential pulses (-280 V) to the first, third, and fifth dynodes during the laser pulse. The gain of the photomultiplier dropped transiently by a factor of 1 x 10(6). The delayed fluorescence showed a smooth but nonexponential decay from 100 ns to 1 ms that was explained by the relaxation of the average free energy between P* and P(+)Q(A)(-) changing from -580 to -910 meV. This relaxation is due to the slow protein response to charge separation and can be described by a Kohlrausch relaxation function with time constant of 65 micros and a stretching exponent of alpha = 0.45. |
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