Interaction of photosynthesis and respiration in Rhodospirillaceae: evidence for two functionally distinct b-c1 complex fractions

Abstract

Flash-induced inhibition (on odd flashes) or reactivation (on even flashes) of respiration in photosynthetic bacteria has been interpreted formerly as resulting from a diversion of electrons from the respiratory pathway to the photosynthetic electron flow via cytochrome c 2 and re-injection of electrons in the respiratory pathway from the Q A Q B photoreduced acceptor (Vermeglio A. and Carrier, J.M. (1984) Biochim. Biophys. Acta 764, 233–238); the model implied that the photooxidation of cytochrome c 2 was strictly concomitant with the rise of respiration inhibition and that this inhibition was of large magnitude. These consequences are not verified experimentally. Instead, when correctly interpreting the oxygen signal kinetics obtained with a new electrode system bringing by centrifugation a thin layerof cells in close contact with a platinum electrode, it is found that the respiration inhibition exhibits kinetics very similar to those of the re-reduction of cytochromes c 1 + c 2 ; also,they are always of small magnitude. A new modelis proposed accounting for the above results: the respiratory and photosynthetic electron pathways are linked through the agency of the ubiquinone pool,not cytochrome c 2 . It is further specified that two populations of b-c 1 complex coexist, one associated with the reaction center and the other with the cytochrome oxidase; thesepopulations do not exchange freely, at least on a time-scale of a few seconds.