The high-affinity binding site for manganese on the oxidizing side of Photosystem II |
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| Institution: | 1. Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse, School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;2. National & Local Joint Engineering Research Center for Mineral Salt Deep Utilization, Key Laboratory for Palygorskite Science and Applied Technology of Jiangsu Province, School of Chemical Engineering, Huaiyin Institute of Technology, Huaian 223003, China;3. Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), Nanjing University of Information Science & Technology, Nanjing 210044, China;1. Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, USA;2. Department of Chemistry and Center for Theoretical Biological Physics, Rice University, Houston, Texas, USA |
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| Abstract: | Electron donation to Photosystem II (PS II) by diphenylcarbazide (DPC) is interrupted by the presence of endogenous Mn in PS II particles. Removal of this Mn by Tris treatment greatly stimulates the electron transport with DPC as donor. Binding of low concentration of exogenous Mn(II) to Tris-treated PS II particles inhibits DPC photooxidation competitively with DPC. This phenomenon was used to locate a highly specific Mn(II) binding site on the oxidizing side of Photosystem II with dissociation constant about 0.15 μM. The binding of Mn(II) is electrostatic in nature. Its affinity depends not only on the ionic strength, but also on the anion species of the salt in the medium. The effectiveness in decreasing the affinity follows the order F? > SO2?4 > CH3COO? > CI? > Br? > NO3?. This observation is interpreted as follows: smaller ions, like F?, CH3COO?, and larger ions, like SO2?4, have inhibitory effects on Mn(II) binding, whereas ions with optimal size, like Cl?, Br? and NO3?, can stabilize the binding, resembling the anion requirement for reactivation of Cl?-depleted chloroplasts. We suggest that the binding site for Mn(II) we observed is the site for the endogenous Mn in the O2-evolving complex of PS II. This site remains after Tris treatment, which removes all the endogenous Mn as well as the three extrinsic proteins, indicating that it is on the intrinsic component(s) of PS II reaction centers. Furthermore, the Cl? requirement for O2 evolution may be attributed, at least partly to its stabilizing effect on Mn binding. |
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