A Cytochrome f/b6 Complex of Five Polypeptides with Plastoquinol‐Plastocyanin‐Oxidoreductase Activity from Spinach Chloroplasts

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Abstract
The isolation of a cytochrome f/b6 complex from spinach chloroplasts with high yield and purity is reported. The complex consists of 5 polypeptides with a MW of 34, 33, 23.5, 20 and 17.5 kDa [kilodaltons], and contains 1 cytochrome f, 2 cytochromes b6 and the Rieske Fe-S center with 2 non-heme irons. It does not contain plastocyanin and is almost completely devoid of chlorophyll and carotenoids, but lipid and detergent are present. It is lacking cytochrome b-559, although 3 of the 5 polypeptides seem to carry heme groups. The preparation has plastoquinol-plastocyanin oxidoreductase activity with plastoquinol-1- and plastoquinol-9, which is sensitive to 2,5-dibromomethylisopropyl-p-benzoquinone, to 2-iodo-6-isopropyl-3-methyl-2'',4,4''-trinitrodiphenyl ether, to 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole, and to bathophenanthroline. Characteristics of this activity with respect to substrate concentrations, pH, detergent effect and other parameters are described.