title: Delayed fluorescence from the photosynthetic reaction center measured by electronic gating of the photomultiplier.
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.
authors.affiliation: Department of Biophysics, University of Szeged, P.O.Box 655, Szeged, Hungary.
authors.forename: Z
authors.initials: Z
authors.lastname: Filus
authors.forename: G
authors.initials: G
authors.lastname: Laczkó
authors.forename: C A
authors.initials: CA
authors.lastname: Wraight
authors.forename: P
authors.initials: P
authors.lastname: Maróti
mesh_terms: D004583:Electrons; D007700:Kinetics; D008856:Microscopy, Fluorescence / Q000379:methods*; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins