Thermal and structural changes of photosynthetic reaction centers characterized by photoacoustic detection with a broad frequency band hydrophone.
Photochem Photobiol
; 74(1): 81-7, 2001 Jul.
Article
en En
| MEDLINE
| ID: mdl-11460542
Photoacoustic measurements using a broad frequency band hydrophone were carried out in photosynthetic reaction centers (RC) isolated from Rhodobacter sphaeroides R-26 purple bacteria. Data were extracted on enthalpy and volume changes accompanying the primary steps after excitation in the range of 0-500 microseconds aimed at further characterizing the thermodynamic properties of the RC. Quinone titration showed that the volume contraction accompanying the electron transport is sensitive to the molecular species occupying the secondary quinone site. delta VM = 14.4, 7.7 and 4.3 cm3 molar volume contractions were calculated from the measured parameters for 1, 2 and 0.07 quinone/RC after light excitation. Comparing the enthalpy changes (delta H) to the Gibbs free energy data in the literature, a rather large (26%) entropic contribution to the free energy changes (delta G) is estimated for the P*QAQB-->P+QA-QB electron transport (where QA and QB represent primary and secondary quinones, respectively). This is in contrast to previous estimations that delta G = delta H in these processes. On the other hand, only a small (4%) entropic contribution to the delta G of the P*QAQB-->P+QAQB- process is estimated, in agreement with the literature data. Our results are in good agreement with the data obtained earlier (Edens et al. [2000] J. Am. Chem. Soc. 122, 1479-1485).
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Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Proteínas del Complejo del Centro de Reacción Fotosintética
Tipo de estudio:
Diagnostic_studies
Idioma:
En
Revista:
Photochem Photobiol
Año:
2001
Tipo del documento:
Article
País de afiliación:
Hungria
Pais de publicación:
Estados Unidos