Alteration of the structure and function of photosystem I by Pb2+
Ahmed Belatik1, Surat Hotchandani, Heidar-Ali Tajmir-Riahi
1Groupe de recherche en biologie végétale, Université du Québec à Trois-Rivières, C.P. 500, Trois-Rivières, Québec, Canada G9A 5H7.
Abstract:
The toxic effects of Pb(2+) on photosynthetic electron transport were studied in photosystem I (PSI) submembrane fractions isolated from spinach. Structural and spectroscopic analysis using FTIR, fluorescence and X-ray photoelectron spectroscopy (XPS) showed that Pb(2+) binds with proteins via oxygen and nitrogen atoms with an overall binding constant of KPb-PSI=4.9×10(3) (±0.2) M(-1) and the number of bound Pb(2+) cation was 0.9 per PSI complex. Pb(2+) binding altered the protein conformation indicating a partial protein destabilization. Electron transport and P700 photooxidation/reduction measurements showed that the interaction of Pb(2+) cations with PSI produced a donor side limitation of electron transport presumably due to Pb(2+) binding to or in the vicinity of plastocyanin.
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