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Photosynthesis Research

, Volume 34, Issue 3, pp 465–477 | Cite as

MOA-stilbene: A new tool for investigation of the reactions of the chloroplast cytochrome bf complex

  • Peter R. Rich
  • Sally A. Madgwick
  • Simon Brown
  • Gebhard von Jagow
  • Ulrich Brandt
Research Articles

Abstract

MOA-stilbene is known to be a specific inhibitor of the Qo site of mammalian cytochrome bc1 complex. We show that it also binds to the chloroplast cytochrome bf complex. Binding to the reduced enzyme induces a red-shift of the Soret and visible absorption bands of the haems b. Steady state and single turnover experiments with thylakoid membranes show that MOA-stilbene promotes additional ‘oxidant-induced reduction’ of the b haems and slows their subsequent dark reoxidation. In single turnover experiments, the associated slow phase of the carotenoid bandshift at 518 nm is only partially decreased in apparent extent and rate. These and other effects are similar to those produced by NQNO, a Qi site effector, and by analogy indicate that MOA-stilbene should also be primarily a Qi-site effector of the cytochrome bf complex. MOA-stilbene has less effect on other parts of the photosynthetic chain. This confers an important advantage on MOA-stilbene in that its effects on the cytochrome bf complex can be studied by using Photosystem II to activate turnover. Myxothiazol displays effects on the cytochrome bf complex which are similar to, but much weaker than, those of MOA-stilbene.

A Q cycle-based model of turnover of the cytochrome bf complex is presented, which can account for several unusual features of kinetic behaviour.

Key words

electron transfer inhibitors myxothiazol Q-cycle thylakoids 

Abbreviations

DBMIB

2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone

duroquinol

2,3,5,6-tetramethyl-p-benzohydroquinone

Ehx

Ambient potential at pHx versus SHE

Emx

Midpoint potential at pH x versus SHE

haem bH

the higher potential haem b of cytochrome b, thought to be associated with the quinone reduction site, Qi, and sometimes termed haem bn

haem bL

the lower potential haem of cytochrome b, thought to be associated with the quinol oxidation site, Qo, and sometimes termed haem bp

HQNO

2-n-heptyl-4-hydroxyquinoline-N-oxide

MOA-stilbene

E-β-methoxyacrylate-stilbene or (E,E)-methyl 3-methoxy-2-(styrylphenyl)propenoate

NQNO

2-n-nonyl-4-hydroxyquinoline-N-oxide

QB (site)

the (binding site of the) secondary quinone acceptor of Photosystem II

Qo site

the quinol oxidation site and site of proton output of the bc and bf complexes (also termed the Qz or Qp site)

Qi site

the quinone reduction site and site of proton input of the bc and bf complexes (also termed the Qc, Qr or Qn site)

SHE

Standard Hydrogen Electrode

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Copyright information

© Kluwer Academic Publishers 1992

Authors and Affiliations

  • Peter R. Rich
    • 1
  • Sally A. Madgwick
    • 1
  • Simon Brown
    • 1
  • Gebhard von Jagow
    • 2
  • Ulrich Brandt
    • 2
  1. 1.Glynn Research InstituteBodminUnited Kingdom
  2. 2.Gustav-Embden-Zentrum der Biologischen ChemieKlinikum der Johann Wolfgang Goethe-UniversitätFrankfurtGermany

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