Donor function of phosphate ions in photosystem 2 |
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Authors: | NV Goncharova MG Goldfeld AG Chetverikov and VI Binyukov |
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Institution: | (1) A.N, Bakh Institute of Biochemistry, Russian Academy of Sciences, Leninski?, Prospekt 33, Moscow, 117071, Russia;(2) N.N, Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygin Street 4, Moscow, 117977, Russia |
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Abstract: | Evidence was obtained for the interaction between the photosystem 2 (PS2) reaction centre (RC) chlorophyll (Chl) P680 and
inorganic phosphate, Pi. The light-induced endogenous basal electron transport to ferricyanide in PS2 depended on endogenous
Pi. The electron transport in phosphate deficient chloroplasts was absent, and could be resumed upon the addition of exogenous
Pi or of the exogenous electron donor, diphenylcarbazide. Some chloroplast Chl molecules were apparently bound with Pi to
a complex via the magnesium atom that was detected by the increase in absorbance in the Chl a absorption maximum at 435 nm
observed after the consumption of endogenous Pi in the photophosphorylation reactions. The electron paramagnetic resonance
(EPR) Signal I, found in the spectra at 77 K after irradiation of frozen samples in chloroplasts poor in endogenous Pi, was
the sum of P700+ and P680+ signals. The P680+ signal disappeared after addition of Pi, diphenylcarbazide or diuron to the
chloroplasts before freezing. In addition, the EPR doublet signal of the phosphate anion radicals was recorded at 77 K after
irradiation in the ethanol solutions of Chl a containing potassium phosphate. The same doublet signal was discovered in the
difference EPR spectrum "chloroplasts minus chloroplasts with diuron" at 77 K after irradation. The results are a possible
evidence of the participation of phosphate ions in the primary light reactions of PS2.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | chloroplasts diuron inhibition EPR spectrum of chloroplasts ferricyanide reduction methylamine NH2Cl phosphate anion radical photosynthetic electron transport |
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