Studies on the structure and function of photosystem I reaction center complex

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1. Photosystem I particles (PSI-200) prepared by the solubilization of spinach thylakoids with Triton X-100 have been treated with a cross-linker, dithiobis(succinimidylpropionate) (DSP) which reacts specifically with amino groups. The cross-linking with DSP is concluded to give a simple method for stabilization of the iron-sulfur centers A and B in PSI-200.2. Irradiation of PSI-200 with high intensity of white light caused a decrease of the electron transport activity from DCIPH_2 to methylviologen and an irreversible bleaching of chlorophyll. The content of P700 was not affected by this treatment. No photoinhibition was, however, shown in PSI complex (Chl/P700 = 40) which was prepared by the solubilization of PSI-200 with Triton X-100, followed by column chromatography on hydroxyl-apatite gel. The column chromatography may give the simple method of PSI preparation for studies on the primary photochemistry.3. PSI reaction center complex was prepared by the heat-treatment of PSI-200 in the presence of ethylene glycol. The complex was mainly composed with three proteins, PSI-A, PSI-B and PSI-K. The trypsin-treatment of the complex reconstituted into liposomes resulted in the formation of three chlorophyll-protein bands with smaller molecular weight than that of the reaction center complex. Two of them contained P700 and A_1. Characterization of the bands thus obtained is now under investigation.