title: Inhibition of energy-transducing functions of chloroplast membranes by lipophilic iron chelators.
abstract: Lipophilic metal chelators inhibit various energy-transducing functions of chloroplasts. The following observations were made 1. Photophosphorylation coupled to any known mode of electron transfer, i.e. whole-chain noncyclic, the partial noncyclic Photosystem I or Photosystem II reactions, or cyclic, is inhibited by several lipophilic chelators, but not by hydrophilic chelators. 2. The light- and dithioerythritol-dependent Mg2+-ATPase was also inhibited by the lipophilic chelators. 3. Electron transport through either partial reaction. Photosystem I or Photosystem II was not inhibited by lipophilic chelators. Whole-chain coupled electron transport was inhibited by bathophenanthroline, and the inhibition was not reversed by uncouplers. The diketone chelators diphenyl propanedione and nonanedione inhibited the coupled, whole-chain electron transport and the inhibition was reversed by uncouplers, a pattern typical of energy transfer inhibitors. The electron transport inhibition site is localized in the region of platoquinone leads to cytochrome f. This inhibition site is consistent with other recent work (Prince et al. (1975) FEBS Lett. 51, 108 and Malkin and Aparicio (1975) Biochem. Biophys. Res. Commun. 63, 1157) showing that a non-heme iron protein is present in chloroplasts having a redox potential near + 290 mV. A likely position for such a component to function in electron transport would be between plastoquinone and cytochrome f. just where our data suggests there to be a functional metalloprotein. 4. Some of the lipophilic chelators induce H+ leakiness in the chloroplast membrane, making interpretation of their phosphorylation inhibition difficult. However, 1-3 mM nonanedione does not induce significant H+ leakiness, while inhibiting ATP formation and the Mg2+-ATPase. Nonanedione, at those concentrations, causes a two- to four-fold increase in the extent of H+ uptake. 5. These results are consistent with, but do not prove, the involvement of a non-heme iron or a metalloprotein in chloroplast energy transduction.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology*; D002736:Chloroplasts / Q000378:metabolism*; D004579:Electron Transport; D004735:Energy Transfer; D004789:Enzyme Activation / Q000187:drug effects; D007501:Iron / Q000378:metabolism*; D009550:Nigericin / Q000494:pharmacology; D010618:Phenanthrolines / Q000494:pharmacology; D010785:Photophosphorylation / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects; D010944:Plants
chemical_list: D002614:Chelating Agents; D010618:Phenanthrolines; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D007501:Iron; D000251:Adenosine Triphosphatases; D009550:Nigericin; D002118:Calcium