The effect of pH on the reduction kinetics of P-680 in tris-treated chloroplasts |
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Authors: | Hlne Conjeaud Paul Mathis |
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Institution: | Serive de Biophysique, Département de Biologie, Centre d'Etudes Nucléaires de Saclay, BP 2, 91190, Gif-Sur-Yuette, France |
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Abstract: | The primary donor of Photosystem II (PS II), P-680, was photo-oxidized by a short flash and its rate of reduction was measured at different pH values by following the recovery of the absorption change at 820 nm in chloroplasts pretreated with a high concentration of Tris. The re-reduction is biphasic with a fast phase (dominant after the first flash) attributed to the donation by a donor, D1, and a slow phase (usually dominant after the second flash) attributed to a back-reaction with the primary acceptor. It is found that pH has a strong influence on the donation from D1 (τ = 2 μs at pH 9, 44 μs at pH 4), but no influence on the back reaction (τ ≈ 200 μs). pH also influences the stability of the charge separation since the contribution of donation from D1 at the second flash increases at lower pH, getting close to 100% at pH 4. |
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Keywords: | Oxygen evolution pH effect Electron transfer Photosystem II Flash absorption spectroscopy (Chloroplast) |
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