Electron transport and photophosphorylation in chloroplasts as a function of the electron acceptor. III. A dibromothymoquinone-insensitive phosphorylation reaction associated with Photosystem II

S. Izawa, J. Michael Gould, Donald R. Ort, P. Felker, N. E. Good

Research output: Contribution to journalArticle

Abstract

Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) is reputed to be a plastoquinone antagonist which prevents the photoreduction of hydrophilic oxidants such as ferredoxin-NADP+. However, we have found that dibromothymoquinone inhibits only a small part of the photoreduction of lipophilic oxidants such as oxidized p-phenylenediamine. Dibromothymoquinone-resistant photoreduction reactions are coupled to phosphorylation, about 0.4 molecules of ATP consistently being formed for every pair of electrons transported. Dibromothymoquinone itself is a lipophilic oxidant which can be photoreduced by chloroplasts, then reoxidized by ferricyanide or oxygen. The electron transport thus catalysed also supports phosphorylation and the P e2 ratio is again 0.4. It is concluded that there is a site of phosphorylation before the dibromothymoquinone block and another site of phosphorylation after the block. The former site must be associated with electron transfer reactions near Photosystem II, while the latter site is presumably associated with the transfer of electrons from plastoquinone to cytochrome f.

Original languageEnglish (US)
Pages (from-to)119-128
Number of pages10
JournalBBA - Bioenergetics
Volume305
Issue number1
DOIs
StatePublished - Apr 27 1973
Externally publishedYes

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Dibromothymoquinone
Photophosphorylation
Phosphorylation
Photosystem II Protein Complex
Chloroplasts
Electron Transport
Electrons
Plastoquinone
Oxidants
Cytochromes f
Ferredoxins
NADP
Adenosine Triphosphate
Oxygen
Molecules

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

Cite this

Electron transport and photophosphorylation in chloroplasts as a function of the electron acceptor. III. A dibromothymoquinone-insensitive phosphorylation reaction associated with Photosystem II. / Izawa, S.; Gould, J. Michael; Ort, Donald R.; Felker, P.; Good, N. E.

In: BBA - Bioenergetics, Vol. 305, No. 1, 27.04.1973, p. 119-128.

Research output: Contribution to journalArticle

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