S-state dependence of the calcium requirement and binding characteristics in the oxygen-evolving complex of photosystem II
| Autor: | Charles F. Yocum, Marcell A. Marosvölgyi, Mohamed Miqyass, Zachary D. Nagel, Hans J. van Gorkom |
|---|---|
| Rok vydání: | 2008 |
| Předmět: |
Functional role
Conformational change Photosystem II Uv absorbance chemistry.chemical_element Oxygen-evolving complex Calcium Sodium Chloride Biochemistry Ion Potassium Chloride Calcium Chloride Spinacia oleracea Binding site Egtazic Acid Plant Proteins Binding Sites Chemistry Photosystem II Protein Complex Hydrogen-Ion Concentration Oxygen Crystallography Kinetics Cadmium Protein Binding |
| Zdroj: | Biochemistry. 47(30) |
| ISSN: | 1520-4995 |
| Popis: | The functional role of the Ca (2+) ion in the oxygen-evolving complex of photosystem II is not yet clear. Current models explain why the redox cycle of the complex would be interrupted after the S 3 state without Ca (2+), but the literature shows that it is interrupted after the S 2 state. Reinterpretation of the literature on methods of Ca (2+) depletion [Miqyass, M., van Gorkom, H. J., and Yocum, C. F. (2007) Photosynth. Res. 92, 275-287] led us to propose that all S-state transitions require Ca (2+). Here we confirm that interpretation by measurements of flash-induced S-state transitions in UV absorbance. The results are explained by a cation exchange at the Ca (2+) binding site that, in the absence of the extrinsic PsbP and PsbQ polypeptides, can occur in minutes in low S-states and in seconds in high S-states, depending on the concentration of the substituting cation. In the S 2(K (+)) or S 2(Na (+)) state a slow conformational change occurs that prevents recovery of the slow-exchange situation on return to a lower S-state but does not inhibit the S-state cycle in the presence of Ca (2+). The ratio of binding affinities for monovalent vs divalent cations increases dramatically in the higher S-states. With the possible exception of S 0 to S 1, all S-state transitions specifically require Ca (2+), suggesting that Ca (2+)-bound H 2O plays an essential role in a H (+) transfer network required for H (+)-coupled electron transfer from the Mn cluster to tyrosine Z. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|