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

Abstract

The isolation of a cytochrome f/b6 complex from spinach chloroplasts, with high yield and purity is reported. The complex consists of five polypeptides with a molecular mass of 34, 33, 23.5, 20 and 17.5 kDa, and contains one cytochrome f, two cytochromes b6 and the Rieske Fe‐S center with two 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 three of the five 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. Copyright © 1981, Wiley Blackwell. All rights reserved