Mechanism of bicarbonate action on photosynthetic electron transport in broken chloroplasts

Wim F.J. Vermaas, Jack J.S. Van Rensen

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

In CO2-depleted chloroplasts electron transport between the Photosystem II electron acceptor Q and plastoquinone is largely suppressed. In the presence of a high concentration of sodium formate (greater than 10 mM), which probably binds to the bicarbonate site, addition of bicarbonate restores the ferricyanide Hill reaction only after incubation in the dark. With lower formate concentrations bicarbonate is able to restore electron transport in the light. The Hill reaction rate in CO2-depleted chloroplasts after bicarbonate addition, divided by the rate in CO2-depleted chloroplasts before bicarbonate addition, shows a sharp optimum at pH 6.5. Furthermore, the rate-limiting step in bicarbonate action is probably diffusion. The results are explained in terms of a hypothetical model: the bicarbonate-binding site is located at the outer side of the thylakoid membrane, but not directly accessible from the 'bulk'. To reach the site from the bulk, the molecule has to pass a channel with negatively charged groups on its side walls. In the light these groups are more negatively charged than in the dark. Therefore, the formate ion cannot exchange for bicarbonate in the light, and a dark period is necessary to enable exchange of formate for bicarbonate.

Original languageEnglish (US)
Pages (from-to)168-174
Number of pages7
JournalBBA - Bioenergetics
Volume636
Issue number2
DOIs
StatePublished - Jul 13 1981
Externally publishedYes

Keywords

  • (Broken pea chloroplast)
  • Bicarbonate action
  • Electron transport
  • Formate action
  • Hill reaction
  • Photosynthesis

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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