Electron flow between photosystem II and oxygen in chloroplasts of photosystem I-deficient algae is mediated by a quinol oxidase involved in chlororespiration

Laurent Cournac, Kevin Redding, Jacques Ravenel, Dominique Rumeau, Eve Marie Josse, Marcel Kuntz, Gilles Peltier

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In Chlamydomonas reinhardtii mutants deficient in photosystem I because of inactivation of the chloroplast genes psaA or psaB, oxygen evolution from photosystem II occurs at significant rates and is coupled to a stimulation of oxygen uptake. Both activities can be simultaneously monitored by continuous mass spectrometry in the presence of 18O2. The light-driven O2 exchange was Shown to involve the plastoquinone pool as an electron carrier, but not cytochrome b6f. Photosystem II-dependent O2 production and O2 uptake were observed in isolated chloroplast fractions. Photosystem II-dependent oxygen exchange was insensitive to a variety of inhibitors (azide, carbon monoxide, cyanide, antimycin A, and salicylhydroxamic acid) and radical scavengers. It was, however, sensitive to propyl gallate. From inhibitors effects and electronic requirements of the O2 uptake process, we conclude that an oxidase catalyzing oxidation of plastoquinol and reduction of oxygen to water is present in thylakoid membranes. From the sensitivity of flash-induced O2 exchange to propyl gallate, we conclude that this oxidase is involved in chlororespiration. Clues to the identity of the protein implied in this process are given by pharmacological and immunological similarities with a protein (IMMUTANS) identified in Arabidopsis chloroplasts.

Original languageEnglish (US)
Pages (from-to)17256-17262
Number of pages7
JournalJournal of Biological Chemistry
Issue number23
StatePublished - Jun 9 2000


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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