Jan 1, 1976

Photoreactions of cytochrome b6 and cytochrome f in chloroplast photosystem I fragments

Zeitschrift Für Naturforschung. Section C: Biosciences
H Böhme


Photosystem I fragments were prepared by digitonin treatment of spinach chloroplasts. The midpoint potential of cytochrome b6 in the fragments is close to 0V, showing a one electron transition. No cytochrome b559 was detectable, neither in difference absorption spectra nor in light-induced absorbance changes. In the absence of added cofactors only cytochrome b6 photoreduction can be observed. This photoreduction is stimulated by ferredoxin. Ferredoxin-NADP+ reductase appears not to be involved in cytochrome b6 reduction. Photooxidation of cytochrome b6 is dependent on plastocyanin addition and inhibited by DBMIB, a plastoquinone antagonist. Addition of plastocyanin restores cytochrome f photooxidation as well, reacting quite specifically in about equimolar concentrations to bound cytochrome f. The stimulation of cytochrome f oxidation is abolished by an antibody prepared against plastocyanin, indicating a surface location of plastocyanin in digitonin treated membranes. Biphasic kinetics of dark-reduction of cytochrome f by ascorbate indicate that part of this cytochrome f is relatively inaccessible in the membrane. After preillumination a monophasic reduction is observed and the slowly oxidized component is absent. Illumination...Continue Reading

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Mentioned in this Paper

Paragreen A
Sodium 2,6-Dichloroindophenol
Ferredoxin-NADP Reductase
Silver Plastocyanin
Sodium Chloride, (24)NaCl

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