May 3, 2011

Listening to PS II: enthalpy, entropy, and volume changes

Journal of Photochemistry and Photobiology. B, Biology
Harvey J M Hou, D Mauzerall

Abstract

Photosystem II, located in the thylakoid membranes of green plants, algae, and cyanobacteria, uses sunlight to split water into protons, electrons, and a dioxygen molecule. The mechanism of its electron transfers and oxygen evolution including the structure of the protein and rates of the S-state cycle has been extensively investigated. Substantial progress has been made; however, the thermodynamics of PS II electron transfer and of the oxygen cycle are poorly understood. Recent progress in thermodynamic measurements in photosynthesis provides novel insights on the enthalpic and entropic contribution to electron transfer in proteins. In this review the thermodynamic parameters including quantum yield, enthalpy, entropy, and volume changes of PS II photochemistry determined by photoacoustics and other laser techniques are summarized and evaluated. Light-driven volume changes via electrostriction are directly related to the photoreaction in PS II and thus can be a useful measurement of PS II activity and function. The enthalpy changes of the reactions observed can be directly measured by photoacoustics. The apparent reaction entropy can also be estimated when the free energy is known. Dissecting the free energy of a photoreaction...Continue Reading

  • References32
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Citations

Mentioned in this Paper

Thermodynamics
Spinach preparation
Benzoquinone
Dioxygen
Photosynthetic Reaction Centers
Thylakoid Membrane
Histidine
Quinones
Complex (molecular entity)
Polydactyly, Preaxial II (Disorder)

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