Electron transport control in chloroplasts. Effects of photosynthetic control monitored by the intrathylakoid pH

A. N. Tikhonov, G. B. Khomutov, E. K. Ruuge, L. A. Blumenfeld

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Abstract

(1) In isolated chloroplasts (class B) electron flow is controlled mainly by the intrathylakoid pH (pHin). A decrease in pHin due to the light-driven injection of protons inside the thylakoid leads to the retardation of electron flow between two photosystems. This effect can be abolished by uncouplers or under photophosphorylation conditions (addition of Mg2+-ADP with Pi); Mg2+-ATP does not influence the steady-state rate of electron flow, (2) The steady-state pH difference, ΔpH, across the thylakoid membrane was estimated from quantitative analysis of the rate of P-700+ reduction. In chloroplasts, without adding Mg2+-ADP, ΔpH increases from 1.6 to 3.2 as the external pH rises from 6 to 9.5. Under the photophosphorylation conditions, ΔpH decreases showing a minimum at the external pH 7.5 (ΔpH {reversed tilde equals} 0.5-1.0). (3) The value of photosynthetic control, K, measured as the ratio of the steady-state rates of P-700+ reduction in the presence of Mg2+-ADP (with Pi) and without adding Mg2+-ADP is dependent on external pH variations, showing a maximum value of K {reversed tilde equals} 3.5 at pHout 7.5. This pH dependence coincides with that of the ADP-stimulated ΔpH decrease. (4) Experiments with spin labels provide evidence that the light-induced changes in the thylakoid membrane are sensitive to the addition of uncouplers and are affected only slightly by the addition of Mg2+-ADP and Pi.

Original languageEnglish
Pages (from-to)321-333
Number of pages13
JournalBBA - Bioenergetics
Volume637
Issue number2
DOIs
Publication statusPublished - Sep 14 1981
Externally publishedYes

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Keywords

  • (Vicia faba chloroplast)
  • ESR
  • Electron transport
  • Intrathylakoid pH
  • Photophosphorylation
  • Photosynthetic control

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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