Transmembrane Electrochemical Proton Gradients in Chloroplasts

The basic ideas of this approach to the problem of energy coupling in biomembranes can be formulated as follows  

The main principles of membrane phosphorylation are the same in chloroplasts, mitochondria, and photosynthetic bacteria. In this section, in order to analyze the role of protonmotive force in the processes of energy transduction in biomembranes, we will focus our attention on the consideration of proton-transport processes in chloroplasts. In thylakoids the ApH is the main component of transmembrane difference in electrochemical potentials of hydrogen ions, AjuH+ = Acp — 2.3(RT/F)ApH. The conductivities of the thylakoid membrane for the majority of cations (Mg , Na ), existing 

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Transmembrane Electrochemical Proton Gradients in Chloroplasts 139 log Jatp... 

The structures of F class and V class ion pumps are sIm liar to one another but unrelated to and more complicated than P-class pumps. F- and V-class pumps contain several different transmembrane and cytosolic subunits. All known V and F pumps transport only protons. In a process that does not Involve a phosphoprotein Intermediate. V-class pumps generally function to maintain the low pH of plant vacuoles and of lysosomes and other acidic vesicles In animal cells by pumping protons from the cytosolic to the exoplasmic face of the membrane against a proton electrochemical gradient. F-class pumps are found In bacterial plasma membranes and In mitochondria and chloroplasts. In contrast to V pumps, they generally function to power the synthesis of ATP from ADP and Pj by movement of protons from the exoplasmic to the cytosolic face of the membrane down the proton electrochemical gradient. Because of their Importance In ATP synthesis in chloroplasts and mitochondria, F-class proton pumps, commonly called ATP synthases, are treated separately In Chapter 8. 

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