Cyt b-559 (Fd) Participating in Cyclic Electron Transport in Spinach Chloroplasts: Evidence for Kinetic Connection with the Cyt b6/f Complex |
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Authors: | Heimann Sebastian; Schreiber Ulrich |
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Institution: | 1 Department of Biological Sciences, Purdue University West Lafayette, Indiana 49707-1392, U.S.A.
2 Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl Botanik I, Universität Würzburg Julius-von-Sachs Platz 2, D-97082 Würzburg, Germany |
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Abstract: | A small fraction of low potential Cyt b-559, amounting to only13% of total Cyt b-559 in spinach chloroplasts, is analyzedwith the help of a highly selective, computer-controlled spectrophotometer,which simultaneously applies 16 pulse modulated narrow bandmeasuring beams with wavelengths in the cytochrome -band (500600nm) for recordings of time resolved difference spectra. ThisCyt b-559 fraction remains oxidized upon dark incubation withascorbate and is reduced upon illumination. It can be reducedby cyclic PSI in an antimycin A-sensitive reaction or in thecourse of antimycin A-insensitive linear electron transportvia the Cyt b6/f complex. Reduction by NADPH in the dark requiresferredoxin. Simultaneous recordings of Cyt b-563 and Cyt f revealclose kinetic connection between this Cyt b-559 fraction andthe low potential chain of the Cyt b6/f complex. These resultsconfirm 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 theposition of the postulated ferredoxin-plastoquinone reductase(FQR) in cyclic electron transport. (Received March 9, 1999; Accepted May 21, 1999) |
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