Mohanty, PSeibert, M1997-06-012009-05-271997-06-012009-05-271997-06-01Mohanty P, Seibert M. Action of K-crown ether on photosystem II electron transport: characterization of the site of action. Indian Journal of Biochemistry & Biophysics. 1997 Jun; 34(3): 241-8http://imsear.searo.who.int/handle/123456789/28020We 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.engBinding SitesChlorophyll --metabolismElectron Transport --drug effectsEthers, Cyclic --pharmacologyEthyldimethylaminopropyl Carbodiimide --pharmacologyKineticsLightLight-Harvesting Protein ComplexesMolybdenum --metabolismOxygen --metabolismPhotosynthesis --drug effectsPhotosynthetic Reaction Center Complex Proteins --chemistryPhotosystem II Protein ComplexPlant Proteins --metabolismSilicon Compounds --metabolismSpinacia oleracea --metabolismJournal Article