title: Inhibition of the water oxidizing complex of photosystem II and the reoxidation of the quinone acceptor QA- by Pb2+.
abstract: The action of the environmental toxic Pb(2+) on photosynthetic electron transport was studied in thylakoid membranes isolated from spinach leaves. Fluorescence and thermoluminescence techniques were performed in order to determine the mode of Pb(2+) action in photosystem II (PSII). The invariance of fluorescence characteristics of chlorophyll a (Chl a) and magnesium tetraphenylporphyrin (MgTPP), a molecule structurally analogous to Chl a, in the presence of Pb(2+) confirms that Pb cation does not interact directly with chlorophyll molecules in PSII. The results show that Pb interacts with the water oxidation complex thus perturbing charge recombination between the quinone acceptors of PSII and the S2 state of the Mn4Ca cluster. Electron transfer between the quinone acceptors QA and QB is also greatly retarded in the presence of Pb(2+). This is proposed to be owing to a transmembrane modification of the acceptor side of the photosystem.
authors.affiliation: Groupe de Recherche en Biologie Végétale, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Belatik
authors.forename: Surat
authors.initials: S
authors.lastname: Hotchandani
authors.forename: Robert
authors.initials: R
authors.lastname: Carpentier
mesh_terms: D002734:Chlorophyll / Q000037:antagonists & inhibitors / Q000378:metabolism; D000077194:Chlorophyll A; D004579:Electron Transport / Q000187:drug effects; D005453:Fluorescence; D007854:Lead / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000187:drug effects; D045332:Photosystem II Protein Complex / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D011809:Quinones / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018724:Spinacia oleracea / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D060431:Thylakoid Membrane Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D020524:Thylakoids / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D014867:Water / Q000378:metabolism*
chemical_list: D045332:Photosystem II Protein Complex; D011809:Quinones; D060431:Thylakoid Membrane Proteins; D014867:Water; D002734:Chlorophyll; D007854:Lead; C029891:lead chloride; D000077194:Chlorophyll A