Involvement of plastoquinone and lipids in electron transport reactions mediated by the cytochrome b6-f complex isolated from spinach

The isolation of a cytochrome b₆-f complex from spinach, which is depleted of plastoquinone (and lipid), is reported. The depleted complex no longer functions as a plastoquinol-plastocyanin oxidoreductase but can be reconstituted with plastoquinone and exogenous lipids. The lipid classes digalactosyldiacylglycerol, phosphatidylglycerol and phosphatidylcholine were active in reconstitution while monogalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol were not. Neither plastoquinone nor lipid alone fully reconstitutes electron transport in the depleted complex. Saturation of plastoquinol-plastocyanin oxidoreductase activity in the depleted complex occurs at 1 plastoquinone per cytochrome f.