Redox-driven chloroplasts

Before proceeding to the next topic, we look at another version of artificial phosphorylation by chloroplasts in the dark, i.e., not driven hyphotoinducedelectron transfer. This new type oftwo stage phosphorylation, called dark oxidation-reduction coupled phosphorylation, was reported by Selman and Psczolla and may be considered as a variant of the postillumination or the acid-base transition types discussed above. The authors found that ATP formation in chloroplasts in the dark can be achieved by an artificial, transmembrane redox reaction using ascorbate as the reductant for ferricyanide trapped inside the chloroplasts, provided it is mediated by a redox carrier such as DAD, DCIP or PMS that liberates protons during its oxidation, as illustrated in the scheme in Figure 13. 

As in earlier experiments with impalement microelectrodes [6,7] giant chloroplasts of P, metallica were used. The thylakoid membrane was osmotically inflated to form large blebs, accessible to patch pipettes. The thylakoid origin of the bleb membrane was established by chlorphyll fluorescence (not shown). Blebt thylakoid membranes show photochemical redox reactions sensitive to external electric fields [8], as well as light-driven [9] and electric field-driven ATPsynthesis [10],... 

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