On the Role of Ferredoxin and Ferredoxin‐NADP+Reductase in Cyclic Electron Transport of Spinach Chloroplasts

Abstract

Antibodies prepared against purified spinach ferredoxin and ferredoxin-NADP⁺ reductase were used as specific inhibitors of electron-transfer reactions dependent on either ferredoxin or ferredoxin-NADP⁺ reductase. The possible role of both electron carriers in cyclic electron transport was checked using cytochrome b₆ photoreactions as indicator. It could be demonstrated that the ferredoxin antibody inhibits cytochrome b₆ photoreduction. Ferredoxin-NADP⁺ reductase, however, appears not to be involved in this pathway: reductase antibody in concentrations sufficient to completely inhibit electron transport to NADP⁺ had no effect on cytochrome b₆ photoreduction. Quantitative treatment of the immunoassay data showed that osmotically shocked chloroplasts contain both bound ferredoxin and ferredoxin-NADP⁺ reductase in concentrations approximately equal to that of cytochrome b₆.