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Effect of encecalin, euparin and demethylencecalin on thylakoid electron transport and photophosphorylation in isolated spinach chloroplasts
Author(s) -
Castañeda Perla,
Mata Rachel,
LotinaHennsen Blas
Publication year - 1998
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/(sici)1097-0010(199809)78:1<102::aid-jsfa93>3.0.co;2-i
Subject(s) - photophosphorylation , electron transport chain , thylakoid , photosystem i , photosystem ii , chloroplast , chemistry , photochemistry , photosynthesis , photosystem , spinach , p680 , cytochrome b6f complex , hill reaction , p700 , proton transport , biophysics , biochemistry , biology , membrane , gene
The major phytotoxic compounds (encecalin, euparin and demethylencecalin) isolated from Helianthella quinquenervis (Hook) A Gray (Asteraceae) were evaluated on different photosynthetic activities in chloroplasts isolated from spinach leaves. ATP synthesis, proton uptake and electron flow (basal, phosphorylating and uncoupled) were inhibited by encecalin and demethylencecalin in a concentration dependent manner, therefore acting as Hill reaction inhibitors. Encecalin and demethylencecalin did not affect photosystem I (electron transport from diaminodurene to methylviologen), but they inhibited photosystem II (from water to 2,5‐dibromo‐3‐methyl‐6‐isopropyl‐1,4‐ p ‐benzoquinone). Since these compounds inhibited electron flow in the photosystem II partial reactions from water to silicomolybdate and from diphenylcarbazide to dichlorophenol‐indophenol, the site of inhibition was located in the span from P 680 to Q A of the electron transport chain. Euparin, inhibited ATP synthesis, proton uptake and basal and phosphorylating electron transports, but it has not effect on uncoupled electron flow from water to methylviologen. Mg 2+ ‐ATPase activity from bound membrane thylakoid chloroplasts was also inhibited by this compound. These results suggested that euparin inhibited phosphorylation in chloroplasts, acting as an energy‐transfer inhibitor. © 1998 Society of Chemical Industry.