2H2O effect on the electron and proton flow in isolated chloroplasts. An indication for lateral heterogeneity of membrane pH

To determine how the actual pH on the membrane surfaces regulate the redox reactions, a study of the electron and proton flow in thylakoids was made in heavy water, in which ²H⁺ has a smaller mobility than ¹H⁺. The decrease of the redox rates by ²H₂O is stronger in coupled than in uncoupled conditions, although the bulk ΔpH is slightly diminished; therefore changing ¹H⁺ by ²H⁺ enhances the electron transfer control. This is particularly so when the two systems are linearly connected: i.e. the plastoquinone pool, not the water-splitting complex, is the main point of the redox chain regulation by ΔpH and of the deuterium action. The role of the proton diffusion barriers is emphasized and the concept of a heterogeneity—accentuated in ²H₂O - of the pH along the membrane is proposed. The corresponding local pH , different at the points of H⁺ active translocation and passive leakage, would be the real factors controlling the membrane-bound processes.