Action of K-crown ether on photosystem II electron transport: characterization of the site of action.
We have investigated the inhibitory effect of K-crown (18-crown-6 potassium picrate) on photosystem II (PSII)-enriched membrane fragments and O2-evolving core complexes. K-crown at 2-4 microM inhibits about half the control level of O2-evolution activity in both types of PSII samples. Oxygen-evolution studies demonstrated that the ether works by inactivating the centres and not by interfering with antenna function or energy transfer to the reaction centre. K-crown does not disrupt binding of the extrinsic proteins associated with O2 evolution nor complex with bound Ca2+ or Cl- cofactors, but rather it directly inhibits electron transfer after the tetrameric Mn cluster. Fluorescence studies on active and Tris-treated samples showed that K-crown does not prevent artificial donors from transferring electrons to PSII but like DCMU inhibits on the acceptor side after QA, the primary quinone acceptor. However, the ether is a leaky inhibitor and may also act as a weak donor when the Mn cluster is not present. Oxygen-production experiments using silicomolybdate as an artificial acceptor (which accepts from both pheophytin and QB in PSII membranes) demonstrated that the inhibition is at or near the DCMU site.
Mohanty
P
P
School of Life Sciences, Jawaharlal Nehru University, New Delhi, India.
Seibert
M
M
D001665:Binding Sites; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D004579:Electron Transport / Q000187:drug effects; D004988:Ethers, Cyclic / Q000494:pharmacology*; D005022:Ethyldimethylaminopropyl Carbodiimide / Q000494:pharmacology; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008982:Molybdenum / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism; D017655:Silicon Compounds / Q000378:metabolism; D018724:Spinacia oleracea / Q000378:metabolism
D004988:Ethers, Cyclic; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D017655:Silicon Compounds; C013250:silicomolybdate; D002734:Chlorophyll; D008982:Molybdenum; D005022:Ethyldimethylaminopropyl Carbodiimide; D010100:Oxygen; D000077194:Chlorophyll A