Two Views on the Problem of Energy Coupling in Biomembranes

Introduction Two Views on the Problem of Energy Coupling in Biomembranes 

ATP synthesis in biomembranes is not directly caused by electron trans- 

On the other hand, it is possible to create conditions which enable us to catalyze the ATP formation without electron transport. It was demonstrated in the early 1960s that the illumination of chloroplasts in the absence of phosphorylation substrates (ADP and Pi) led to the formation of a certain energized compound (or state), which was capable of providing ATP synthesis in the dark after ADP and Pi addition [17, 18]. This post-illumination ATP synthesis is one of the most explicit demonstrations of the existence in chloroplasts of a high-energy state formed in the light. Later, Jagendorf and 

Uribe demonstrated that such (or similar) a macroergic state can be created artificially as a result of the acid-base transition chloroplasts preincubated at a low pH value in the dark were able to produce ATP from ADP and Pi after a fast pH increase [19]. The ATP formation, coupled to artificially generated macroergic states in chloroplasts, mitochondria, and submitochondrial particles, chromatophores, and reconstituted model systems (lipid vesicles encrusted with ATPsynthase complexes but free of ETC) was studied in more detail by several groups of investigators (see, for references, [20-35]). 

As a matter of fact, the difference in understanding the role of protons in membrane phosphorylation reflects the existence of two different principal approaches to the problem of energy coupling in biomembranes that involve numerous concrete models. The first of them is most clearly expressed in the widely accepted Mitchell chemiosmotic concept [39, 40, 45, 46]. According to Mitchell s postulate, X represents a transmembrane difference in the electrochemical potential of hydrogen ions, A/Ih+- This value can be presented in the form of the sum of two separately measured quantities A/Ih+ = Aq -h (RT/F) ln([H ]i /[H ], , t), where Aq = — Pout is a transmembrane 

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