Abstract
Phosphorylation in chloroplasts is generally accepted to be driven by the electrochemical proton gradient across the thylakoid membrane as proposed by the chemiosmotic theory. However, the relation between the magnitude of the proton motive force (pmf) and the rate of phosphorylation cannot be predicted by chemiosmosis as mechanistic details of energy transduction are required for this purpose. Experiments indicate that both the phosphorylation rate and the phosphorylation potential, (ATP)/(ADP) ⋅ (Pi), increase with increasing the pmf under a variety of conditions (e.g. Avron, 1978). However, other studies indicate that there may not exist an one-to-one relation between the rate of phosphorylation and the magnitude of the pmf. Thus, it was reported that the rate of ATP-synthesis in submitochondrial particles decreases at a constant pmf (Sorgato et al., 1980). More drastic, it was shown that the phosphorylation rate ‘in chloroplasts increased at a diminished pmf (Giersch, 1981). A number of related observations can be found in the literature (e.g., Degani, Shavit, 1972; Wei et al., 1980). However, generally the mere observation was reported, and the findings were not discussed in terms of energy transduction. Stimulation of phosphorylation under conditions where the pmf was expected to be decreased was observed repeatedly but apparently never studied in detail.
Published Version
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