title: Stoichiometry of proton uptake in isolated pea chloroplasts under different light intensities.
abstract: The number of protons released inside the chloroplast thylakoids per electron which is transferred through the electron transport chain (H+/e- ratio) was measured in isolated pea chloroplasts at pH 6.0 under continuous illumination and with methyl viologen as an electron acceptor. At saturating light intensity (200 W X m-2) ("strong" light) the H+/e- ratio was 3. At low intensity (0.9 W X m-2) ("weak" light) the H+/e- ratio was 2 with dark-adapted chloroplasts, but it was close to 3 with chloroplasts that were preilluminated with strong light. It is shown that the presence of azide in the reaction mixture leads to errors in the determination of the H+/e- ratio due to underestimation of the initial rate of H+ efflux on switching off the light. To explain the above data, we assume that transformation of the electron transport chain occurs during illumination with strong light, namely, the Q cycle becomes operative.
mesh_terms: D001386:Azides / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D002736:Chloroplasts / Q000378:metabolism*; D004579:Electron Transport / Q000187:drug effects; D007887:Fabaceae; D008029:Lighting; D008433:Mathematics; D010788:Photosynthesis; D010946:Plants, Medicinal; D011522:Protons
chemical_list: D001386:Azides; D011522:Protons