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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 → S1 and 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 /S1 ratio, 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 → S1 change. 相似文献
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