In this paper the authors emphasise that the proton translocating ATP synthase from thiol-modulated chloroplasts and two cyanobaeterial strains has a coupling ratio of 4 protons per ATP synthesised or hydrolysed. This ratio is determined by several thermodynamic studies at equilibrium between phosphate potential (AGp) and proton gradient (zl/iu+), and is confirmed by measurement of proton flux during ATP hydrolysis. Ratios lower than 4 H+IATP that have been published in the past have predominantly been determined with the oxidised chloroplast enzyme. Errors in these measurements will be discussed.

The ATP-synthesis and the electric phenomena on the thylakoid membrane have been studied under excitation of photosynthesis with short flash groups. The light induced electric potential difference has been measured by means of field indicating absorption changes around 623 nm.It is shown that upon excitation with short %ash groups a certain electric potential difference is required before ATP can be synthesized. Moreover it is confirmed that the ATP-synthesis is accompanied by an additional flux of protons down their electrochemical potential gradient. Correlation between the number of protons which have flowed across the ATPase coupled pathway, and the number of ATP-molecules which have been formed, yields a ratio H+/ATP = 3.Since this ratio includes only those protons, which have interacted with the ATPase complex, it represents the lower limit for H+/ATP-ratios determined by any other method.The necessity of a certain electric potential difference and the fact that 3 H+ have to be translocated down their electrochemical potential difference before one molecule of ATP can be synthesized is consistent with the chemiosmotic postulate, that the ADP N P bond energy is derived from the electrochemical potential difference of the proton across the coupling membrane.With respect to the alternative hypothesis for phosphorylation, the results impose grave restriction on a phosphorylation driven only by the free energy of a chemical intermediate, The main difference between this modSed chemical hypothesis and the chemiosmotic one lies in the possibility of a "direct squiggle phosphorylation" in the former one, while the latter predictsTthat phosphorylation occurs only with an intermediate electrochemical potential difference.I n this paper we question whether such a "direct squiggle phosphorylation" does exist, or if this cannot be answered conclusively, we shall try, to derive limiting properties for the as yet unspecified "direct squiggle phosphorylation". This paper will not be concerned with any squiggle which may operate in series with or cooperate in parallel with and necessarily linked to a chemiosmotic mechanism. Moreover it shall be completely ignored

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F0F1-ATP synthase uses proton-motive force to produce ATP from ADP and Pi. With regard to its rotary mechanics, this energy transducing molecular machine assumes a unique position among all enzymes. In the work presented here we put forward a detailed functional model which is based on experimental results obtained with ATP synthase from spinach chloroplasts. We focus on the role of the elastic element, realized by the stalk-like subunit gamma, whose function is energy transduction between F0 and F1 taking into account the H+/ATP coupling ratio of four. Fitting parameters are the rate constants and the torsional rigidity of gamma, which have been adjusted according to the experimental results where the influence of transmembrane DeltapH on the rates of ATP synthesis/hydrolysis is put to the test. We show that the input and output of torsional energy are regulated by purely statistical principles, giving rise to the amount of transiently stored energy to be sliding, depending on DeltapH. During conditions of maximal turnover gamma turns out to be wound up towards 102 degrees which corresponds to a torque of 5.3. 10-20 N.m.