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.

Reactions of Antibodies against Ferredoxin, Ferredoxin‐NADP+ Reductase and Plastocyanin with Spinach Chloroplasts

“…The inhibitory properties of the antisera and the corresponding test reactions (a, cytochrome-c reduction by NADPH, b, NADP'-photoreduction, c, cytochrome-b, photoreduction) are described in detail in a preceding paper [9]. A similar immunization scheme was used for preparation of the plastocyanin antibody.…”

“…Immunization of the rabbits by highly purified ferredoxin and ferredoxin-NADP' reductase followed the procedure of [9]. The inhibitory properties of the antisera and the corresponding test reactions (a, cytochrome-c reduction by NADPH, b, NADP'-photoreduction, c, cytochrome-b, photoreduction) are described in detail in a preceding paper [9].…”

“…Chloroplasts were isolated from spinach (variety Atlanta), grown under controlled climate conditions as described [9]. These chloroplasts are without the outer envelope and are well coupled to phosphorylation.…”

“…+ reductase and ferredoxin Reaction conditions are described in [9]. For the cytochrome-c reduction (A) the ferredoxin-assay contained (per ml); 30 pmol ferredoxin, 16.3 pmol reductase; the reductase assay: 185 pmol ferredoxin, 9.5 pmol reductase.…”

“…Properties of antisera against ferredoxin-NADP ' reductme, ferredoxin and plastocyanin Details of agglutination and precipitation reactions are described in Methods. Tests for inhibition of enzymatic activity of reductase or ferredoxin, cytochrome-c reduction by NADPH, NADP+-photoreduction by chloroplasts [9]; for plastocyanin: cytochrome-fphotooxidation by photosystem I fragments [I 31, oxygen uptake by chloroplasts ( …”