Biochemical Evidence that the Higher Plant Photosystem II Core Complex is Organized as a Dimer

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multiprotein core complex of higher plant PS II has been examined. Oxygen-evolving PS II particles or thylakoid membranes of wild-type and Chl b-less barley were extracted with various glycosidic surfactants and electrophoretically fractionated. The predominant multiprotein core complex II (CC II) fractions had sizes on gel electrophoresis of M_r=230,000 and M_r= 140,000 and were photochemically active. Both fractions had identical absorption spectra, contained the beta-carotene-chl a-proteins (Cp47 and Cp43), the PS II reaction center subunits (D1 and D2), and the two cytochrome b_<559> subunits in unit stoichiometry. The M_r= 230,000 fraction could evolve oxygen in the light and contained an M_r=33,000 oxygen evolution enhancer (OEE 33) polypeptide, whereas the M_r= 140,000 fraction lacked OEE 33 and could not evolve oxygen. The apparent sizes of the two fractions were also estimated by gel filtration as M_r=490,000 and M_r= 220,000, respectively; the estimates by gel filtration more accurately reflect their predicted sizes. Further analyses by nondenaturing gel electrophoresis indicated that Cp47, Cp43 and the three OEE gene products probably occur as homodimers in situ. Our data suggest that phosphorylation of CC II subunits occurs when they are located in the oligomeric form. We propose that the native state of the PS II core complex in higher plants is dimeric, and that this state, which was previously observed only in thermophilic cyanobacteria, is probably the form present in all oxygenic organisms.
日本植物生理学会の論文

Biochemical Evidence that the Higher Plant Photosystem II Core Complex is Organized as a Dimer

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