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On an Inhibitor of Ferredoxin Catalyzed Cyclic Photophosphorylation in Thylakoid Membranes *
Author(s) -
Trebst Achim,
Wietoska Helga
Publication year - 1989
Publication title -
botanica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0932-8629
DOI - 10.1111/j.1438-8677.1989.tb00109.x
Subject(s) - photophosphorylation , ferredoxin , thylakoid , cytochrome b6f complex , photosystem i , plastoquinone , cytochrome , antimycin a , electron transport chain , chemistry , dcmu , photochemistry , chloroplast , photosystem ii , biochemistry , photosynthesis , enzyme , gene
Dibromo‐ and diiodo‐naphthoquinones are shown to be inhibitors of the cytochrome b 6 /f complex in isolated thylakoid membranes from spinach chloroplasts. Dibromo‐naphthoquinone inhibits ferredoxin catalyzed cyclic photophosphorylation at 0.1 μM concentrations, but non cyclic e‐flow only at 10 μM. It does not inhibit cyclic systems with artifical cofactors, nor non‐cyclic electron flow from duroquinol through photosystem I via the cytochrome b 6 /f complex. Dibromo‐naphthoquinone does however, lower the stoichiometry for ATP formation in the duroquinol donor system. This inhibitory pattern is quite different from that of DBMIB, but very similar to that of antimycin. This antimycin‐like behaviour of these inhibitors is interpreted to indicate a) the existence of a Q c site in the cytochrome b 6 /f complex and its obligate function in ferredoxin catalyzed cyclic electron flow and b) a non‐essential role of the Q c site in non‐cyclic electron flow, but which — when operative — pumps an extra proton across the thylakoid membrane increasing the ATP yield.