Identification of the polypeptides in the cytochromeb 6/f complex from spinach chloroplasts with redox-center-carrying subunits |
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Authors: | Eduard Hurt Günter Hauska |
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Affiliation: | (1) Institut für Botanik, Universität Regensburg, Germany;(2) Institut für Botanik, Universität Regensburg, Universitätsstrabe 31, 8400 Regensburg, Germany |
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Abstract: | An improved procedure for the isolation of the cytochromeb6/f complex from spinach chloroplasts is reported. With this preparation up to tenfold higher plastoquinol-plastocyanin oxidoreductase activities were observed. Like the complex obtained by our previous procedure, the complex prepared by the modified way consisted of five polypeptides with apparent molecular masses of 34, 33, 23, 20, and 17 kD, which we call Ia, Ib, II, III, and IV, respectively. In addition, one to three small components with molecular masses below 6 kD were now found to be present. These polypeptides can be extracted with acidic acetone. Cytochromef, cytochromeb6, and the Rieske Fe-S protein could be purified from the isolated complex and were shown to be represented by subunits Ia + Ib, II, and III, respectively. The heterogeneity of cytochromef is not understood at present. Estimations of the stoichiometry derived from relative staining intensities with Coomassie blue and amido black gave 1:1:1:1 for the subunits Ia + Ib/II/III/IV, which is interesting in of the presence of two cytochromesb6 per cytochromef. Cytochromef titrated as a single-electron acceptor with a pH-independent midpoint potential of +339 mV between pH 6.5 and 8.3, while cytochromeb6 was heterogeneous. With the assumption of two components present in equal amounts, two one-electron transitions withEm(1)=–40 mV andEm(2)=–172 at pH 6.5 were derived. Both midpoint potentials were pH-dependent.Abbreviation Tris tris(hydroxymethyl)aminomethane - SDS sodium dodecylsulfate - SDS-PAGE SDS polyacrylamide gel electrophoresis - MES 2-(N-morpholino)ethanesulfonic acid |
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Keywords: | Cytochromeb6/f complex heterogeneity of cytochromef isolation of cytochromef isolation of cytochromeb6 redox titration pH-dependent midpoint potential of cytochromeb6 |
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