Cyt b-559 (Fd) Participating in Cyclic Electron Transport in Spinach Chloroplasts : Evidence for Kinetic Connection with the Cyt b_6/ƒ Complex

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A small fraction of low potential Cyt b-559, amounting to only 13% of total Cyt b-559 in spinach chloroplasts, is analyzed with the help of a highly selective, computer-controlled spectrophotometer, which simultaneously applies 16 pules modulated narrow band measuring beams with wavelengths in the cytochrome α-band (500-600 nm) for recordings of time resolved difference spectra. This Cyt b-559 fraction remains oxidized upon dark incubation with ascorbate and is reduced upon illumination. It can be reduced by cyclic PSI in an antimycin A-sensitive reaction or in the course of antimycin A-insensitive linear electron transport via the Cyt b_6/ƒ complex. Reduction by NADPH in the dark requires ferredoxin. Simultaneous recordings of Cyt b-563 and Cyt ƒ reveal close kinetic connection between this Cyt b-559 fraction and the low potential chain of the Cyt b_6/ƒ complex. These results confirm and extend previous observations of Miyake et al.1995 (Plant Cell Physiol.36: 743) in maize mesophyll thylakoids, which led to the hypothesis that Cyt b-559 (Fd) occupies the position of the postulated ferredoxin-plastoquinone reductase (FQR) in cyclic electron transport.
日本植物生理学会の論文