The A^-F_Xto F_A/BStep inSynechocystis6803 Photosystem I Is Entropy Driven

Abstract

We have previously reported the enthalpy and volume changes of charge separation in photosystem

Enthalpy, Entropy, and Volume Changes of Electron Transfer Reactions in Photosynthetic Proteins

“…However, one weakness of the theory is the omission of entropic contribution in the electron transfer steps. The recent experimental results pointed out the crucial role of entropy change in chemical and biological systems (Feitelson & Mauzerall, 1996;Edens et al, 2000;Crovetto et al, 2006;Hou & Mauzerall, 2006). The follow-up and extensive thermodynamic measurements especially by photoacoustics is worth while.…”

“…For a given photoreaction, the accessible parameters include the molecular volume change secondary to conformational change or electrostriction, and enthalpy changes. With the measurement of enthalpy change by pulsed photoacoustics, the reaction entropy can be calculated when free energy is known (Feitelson & Mauzerall, 1996;Edens et al, 2000;Hou & Mauzerall, 2006). Figure 3 shows the experimental setup of the pulsed photoacoustic apparatus, which enables one to determine the volume change and enthalpy of photoreactions on the nanosecond to microsecond time scales.…”

“…Deconvolution analysis of a typical photoacoustic pressure wave to time-resolve the enthalpy and volume changes of two individual electron transfer steps in PS I of Synechocystis sp. PCC 6803 (reproduced with permission from the American Chemical Society (Hou & Mauzerall, 2006)). …”

“…These discrepancies in purified complexes from different organisms such as Synechocystis, Chlamydomonas, and spinach chloroplasts must be clarified. We previously determined the volume changes and enthalpy changes of electron transfer in Synechocystis PS I complexes on the microsecond time scale ) and then timeresolved two individual steps in the complexes on the nanosecond time scale (Hou & Mauzerall, 2006). A significant entropic component was found.…”

Probing the Thermodynamics of Photosystem I by Spectroscopic and Mutagenic Methods

“…Pulsed photoacoustic spectroscopy can provide a direct measurement of thermodynamic parameters such as volume change and enthalpy changes that accompany electron transfer reactions (Braslavsky, 1985;Carpentier et al, 1990;Arnaut et al, 1992;Small et al, 1992;Losi et al, 1995;Edens et al, 2000;Malkin, 2000;Herbert et al, 2001;Feitelson and Mauzerall, 2002;Delosme, 2003;Hou and Mauzerall, 2006;Hou and Sakmar, 2010;Hou and Mauzerall, 2011). With prior knowledge of the change in Gibbs free energy of the corresponding reactions, the apparent entropy change (TS) of the reaction can be calculated.…”