Spin-probes designed for measuring the intrathylakoid pH in chloroplasts

Spin-probes designed for measuring the intrathylakoid pH in chloroplasts Full article

Journal

Biochimica et Biophysica Acta - Bioenergetics
ISSN: 0005-2728 , E-ISSN: 0006-3002

Output data

Year: 2008, Volume: 1777, Number: 3, Pages: 285-294 Pages count : 10 DOI: 10.1016/j.bbabio.2007.12.002

Tags

chloroplast; electron paramagnetic resonance; spin-probes; transthylakoid proton gradient

Authors

Tikhonov Alexander N. ¹ , Agafonov Roman V. ¹ , Grigor'ev Igor A. ² , Kirilyuk Igor A. ² , Ptushenko Vasilii V. ¹ , Trubitsin Boris V. ¹

Affiliations

1	(Данные Web of science) Moscow MV Lomonosov State Univ, Fac Phys, Dept Biophys, Moscow 119992, Russia
2	(Данные Web of science) Novosibirsk Organ Chem Inst, Novosibirsk, Russia

Nitroxide radicals are widely used as molecular probes in different fields of chemistry and biology. In this work, we describe pH-sensitive imidazoline- and imidazolidine-based nitroxides with pK values in the range 4.7-7.6 (2,2,3,4,5,5-hexamethylperhydroimidazol-1-oxyl, 4-amino-2,2,5,5-tetramethyl-2,5-dihydro-1H-imidazol-1-oxyl, 4-dimethylamino-2,2-diethy1-5,5-dimethyl-2,5-dihydro-1H-imidazol-1-oxyl, and 2,2-diethyl-5,5-dimethyl-4-pyrrolidyline-1-yl-2,5-dihydro-1H-imidazol-1-oxyl), which allow the pH-monitoring inside chloroplasts. We have demonstrated that EPR spectra of these spin-probes localized in the thylakoid lumen markedly change with the light-induced acidification of the thylakoid lumen in chloroplasts. Comparing EPR spectrum parameters of intrathylakoid spin-probes with relevant calibrating curves, we could estimate steady-state values of lumen pH(in) established during illumination of chloroplasts with continuous light. For isolated bean (Vicia faba) chloroplasts suspended in a medium with pH(out) = 7.8, we found that pH(in) approximate to 5.4-5.7 in the state of photosynthetic control, and pH(in) approximate to 5.7-6.0 under photophosphorylation conditions. Thus, ATP synthesis occurs at a moderate acidification of the thylakoid lumen, corresponding to transthylakoid pH difference Delta pH approximate to 1.8-2.1. These values of Delta pH are consistent with a point of view that under steady-state conditions the proton gradient Delta pH is the main contributor to the proton motive force driving the operation of ATP synthesis, provided that stoichiometric ratio H+/ATP is n >= 4-4.7. (C) 2007 Elsevier B.V. All rights reserved.

Tikhonov A.N. , Agafonov R.V. , Grigor'ev I.A. , Kirilyuk I.A. , Ptushenko V.V. , Trubitsin B.V.
Spin-probes designed for measuring the intrathylakoid pH in chloroplasts

Biochimica et Biophysica Acta - Bioenergetics. 2008. V.1777. N3. P.285-294. DOI: 10.1016/j.bbabio.2007.12.002 WOS Scopus РИНЦ

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Mar 1, 2008

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