Stoichiometry of Proton Translocation during Photosynthesis

Formation of ATP in photosynthesis takes place at the expense of free energy stored in the gradient of protons across the thylakoid membrane. Set up of the proton gradient is accomplished by the light‐driven electron transport reactions. The stoichiometry of H + translocation across the thylakoid membrane is determined with respect to electron flow and ATP synthesis. Direct information is obtained on the basis of the H + flux measurement. Depending on the experimental conditions two or three H + are translocated from outside into the aqueous inner phase of the thylakoid vesicles for each electron which is transferred through the electron transport chain. Three H + are translocated from inside to outside across the ATPase for each ATP molecule which is synthesized. Mechanistic and energetic consequences are discussed.