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Studies on well-coupled Photosystem-I-endriched subchloroplast vesicles. Electron transfer by b- and c-type cytochromes in relation to the origin of the "slow" electric potential component
Ist Teil von
Biochimica et biophysica acta, Protein structure and molecular enzymology, 1984-01, Vol.766 (1), p.179-187
Erscheinungsjahr
1984
Link zum Volltext
Quelle
Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)
Beschreibungen/Notizen
Cytochrome redox changes and electric potential generation are kinetically compared during cyclic electron transfer in Photosystem-I-enriched and Photosystem-II-depleted subchloroplast vesicles (i.e., stroma lamellae membrane vesicles) supplemented with ferrodoxin with ferredoxin using a suitable electron donating system. Per flash two cytochrome b-563 species turn over for one cytochrome c-554. The fast reductive pathway proceeds probably via ferredoxin, is insensitive to DNP-INT, DBMIB and HQNO and is independent on the dark redox state of the electron transfer chain. In contrast, the slow reductive pathway is sensitive to DNP-INT and DBMIB, is strongly delayed at suboptimal redox poising (i.e., low NADPH.NADP super(+) ratio) and is possibly coupled to the reduction of cytochrome c-554. Also cytochrome b-559 sub(LP) (LP, low potential) is involved in Photosystem-I-associated cyclic electron flow, but its flash-induced turnover is only observed at low preestablished electron pressure on the electron-transfer chain. Data suggest that cyclic electron flow around Photosystem I only proceeds if cytochrome b-559 sub(LP) is in the reduced state before the flash, and a tentative model is presented for electron transfer through the cyclic system.