Transmembrane Electron Transport in Ascorbate-loaded Plasma Membrane Vesicles from Higher Plants Involves a B-type Cytochrome

The possible involvement of a high-potential b-type cytochrome in plasma membrane electron transport was tested using ascorbate-loaded membrane vesicles. Absorption spectra demonstrated that the cytochrome was about 89% reduced in these preparations. Use of ascorbate oxidase and washing of the vesicles further indicated that reduction was mediated by intra-vesicular ascorbate. Addition of low concentrations of ferricyanide caused a rapid cytochrome oxidation followed by a slower re-reduction. The kinetics of this response indicate that the electron acceptor was fully reduced before re-reduction of the cytochrome occurred. These observations suggest that the b-type cytochrome mediates transmembrane electron transfer.