DIFFERENCE SPECTRA OF THE OXIDIZED INTERMEDIATES IN THE PHOTOSYNTHETIC OXYGEN-EVOLVING SYSTEM: EVIDENCE FOR A SMALL S0→S1 ABSORPTION CHANGE |
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Authors: | Jearome Lavergne |
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Institution: | Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France |
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Abstract: | A consensus has emerged in the recent literature on the fact that the UV difference spectrum of the first oxidation step (S0→ S1) of the photosynthetic oxygen-evolving complex is significantly different and generally smaller than the spectra of the higher oxidation steps (S0→ S1and S2→ S3). Discrepancies still persist, however, notably in the 300 nm region where the S0→ S1 change was either reported to be markedly smaller than the other changes, or, at variance, to have a similar amplitude. A novel approach is proposed here for estimating the ratio of these changes, requiring no estimate of the Kok model parameters, such as the initial S0/S1ratio, or damping coefficients. This was achieved by comparing the absorption difference between two fully deactivated states, differing only in their S0/S1, distribution, with the flash-induced changes measured from these states. The results show that, at two wavelengths around 300 nm, the S0→ S1 change is at least 4 times, and probably 5–6 times smaller than the S0→ S1change. |
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