Phosphorylation in isolated chloroplasts coupled to dichlorophenyldimethylurea-insensitive silicomolybdate reduction |
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Authors: | Luciana Rosa DO Hall |
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Institution: | Department of Plant Sciences, University of London, King''s College, 68 Half Moon Lane, London SE24 9JF U.K. |
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Abstract: | 1. The electron transport in isolated chloroplasts with silicomolybdate as electron acceptor has been reinvestigated. The silicomolybdate reduction has been directly measured as ΔA750 or indirectly as O2 evolution (in the presence or absence of ferricyanide).2. Silicomolybdate-dependent O2 evolution is inhibited to a similar extent by 3-(3,4-dichlorophenyl) 1, 1-dimethylurea (DCMU) or dibromothymoquinone (DBMIB), indicating the existence of two different sites of silicomolybdate reduction: one before the DCMU block (i.e. at Photosystem II) and one after the DBMIB block (i.e. at Photosystem I).3. Silicomolybdate-dependent O2 evolution is coupled to ATP synthesis with an ratio of 1.0 to 1.1. The presence of ferricyanide inhibits this ATP synthesis ( ratio then is about 0.3).4. Silicomolybdate-dependent O2 evolution is also coupled to ATP-synthesis in the presence of DCMU with an ratio of 0.6–0.8 characteristic of Site II; in this case the electron transport itself is not affected by uncouplers or energy-transfer inbihitors.5. The data are interpreted as a further demonstration that the water-splitting reaction is responsible for the conservation of energy at Photosystem II. |
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Keywords: | DBMIB DCMU 3-(3 4-dichlorophenyl)-1 1-dimethylurea DABS diazonium benzene sulfonate DAD MES HEPES Tris tris (hydroxymethyl) amino methane |
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