TY - JOUR
T1 - Nanosecond fluorescence from isolated photosynthetic reaction centers of Rhodopseudomonas sphaeroides
AU - Woodbury, Neal W.T.
AU - Parson, William W.
N1 - Funding Information:
We thank Drs. E. Schlodder, R. van Grondelle, J. Thomas and J. Shibata for assistance in developing the experimental protocol and for helpful discussions, Drs. G. Feher, D. Kleinfeld, S. Boxer and D. Holten for access to unpublished manuscripts, and J. Rutberg and M. Remeroski for preparation of reaction centers. This work was supported by NSF grant PCM 8016593. N. Woodbury was supported in part by Public Health Service National Research Service Award GM 07270 from the National Institutes of Health.
PY - 1984/11/26
Y1 - 1984/11/26
N2 - The time-course of fluorescence from reaction centers isolated from Rhodopseudomonas sphaeroides was measured using single-photon counting techniques. When electron transfer is blocked by the reduction of the electron-accepting quinones, reaction centers exhibit a relatively long-lived (delayed) fluorescence due to back reactions that regenerate the excited state (P*) from the transient radical-pair state, PF. The delayed fluorescence can be resolved into three components, with lifetimes of 0.7, 3.2 and 11 ns at 295 K. The slowest component decays with the same time-constant as the absorbance changes due to PF, and it depends on both temperature and magnetic fields in the same way that the absorbance changes do. The time-constants for the two faster components of delayed fluorescence are essentially independent of temperature and magnetic fields. The fluorescence also includes a very fast (prompt) component that is similar in amplitude to that obtained from unreduced reaction centers. The prompt fluorescence presumably is emitted mainly during the period before the initial charge-transfer reaction creates PF from P*. From the amplitudes of the prompt and delayed fluorescence, we calculate an initial standard free-energy difference between P* and PF of about 0.16 eV at 295 K, and 0.05 eV at 80 K, depending somewhat on the properties of the solvent. The multiphasic decay of the delayed fluorescence is interpreted in terms of relaxations in the free energy of PF with time, totalling about 0.05 eV at 295 K, possibly resulting from nuclear movements in the electron-carriers or the protein.
AB - The time-course of fluorescence from reaction centers isolated from Rhodopseudomonas sphaeroides was measured using single-photon counting techniques. When electron transfer is blocked by the reduction of the electron-accepting quinones, reaction centers exhibit a relatively long-lived (delayed) fluorescence due to back reactions that regenerate the excited state (P*) from the transient radical-pair state, PF. The delayed fluorescence can be resolved into three components, with lifetimes of 0.7, 3.2 and 11 ns at 295 K. The slowest component decays with the same time-constant as the absorbance changes due to PF, and it depends on both temperature and magnetic fields in the same way that the absorbance changes do. The time-constants for the two faster components of delayed fluorescence are essentially independent of temperature and magnetic fields. The fluorescence also includes a very fast (prompt) component that is similar in amplitude to that obtained from unreduced reaction centers. The prompt fluorescence presumably is emitted mainly during the period before the initial charge-transfer reaction creates PF from P*. From the amplitudes of the prompt and delayed fluorescence, we calculate an initial standard free-energy difference between P* and PF of about 0.16 eV at 295 K, and 0.05 eV at 80 K, depending somewhat on the properties of the solvent. The multiphasic decay of the delayed fluorescence is interpreted in terms of relaxations in the free energy of PF with time, totalling about 0.05 eV at 295 K, possibly resulting from nuclear movements in the electron-carriers or the protein.
KW - (Rps. sphaeroides)
KW - Bacterial photosynthesis
KW - Fluorescence kinetics
KW - Reaction center
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U2 - 10.1016/0005-2728(84)90205-6
DO - 10.1016/0005-2728(84)90205-6
M3 - Article
C2 - 6333897
AN - SCOPUS:0021741695
SN - 0005-2728
VL - 767
SP - 345
EP - 361
JO - BBA - Bioenergetics
JF - BBA - Bioenergetics
IS - 2
ER -