Charge Distribution on the Membrane Surface of the Donor side of Photosystem II. Effect of the Free Radical Relaxing Agent Dysprosium on the Power Saturation of EPR Signal II_s in PS-II Particles

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The effect of the paramagnetic rare earth dysprosium (Dy) on the power saturation of EPR Signal II_s was studied with the PS-II particles to obtain information on the charge distribution and structure of the donor side of PS II, which contains the three peripheral polypeptides of 33, 24 and 18 kDa. DyCl_3 and Dy-EDTA complex were used as relaxing agents for Signal II_s in the untreated, NaCl-washed and CaCl_2-washed PS-II particles. In the untreated PS-II particles, DyCl_3 significantly relieved the power saturation of Signal II_s, whereas Dy-EDTA was less effective. After the NaCl washing of the PS-II particles, which removed the 24- and 18-kDa polypeptides, the effectiveness of DyCl_3 increased while that of Dy-EDTA did not change. In the CaCl_2-washed particles, from which all the three polypeptides had been removed, DyCl_3 was slightly more effective and Dy-EDTA was more effective than in the NaCl-washed particles. These results suggest that the binding site of the 24- and/or 18-kDa polypeptides on the inner surface of PS II is negatively charged, while the binding site of the 33-kDa polypeptide is positively charged.
日本植物生理学会の論文