In situ characterisation of photosynthetic electron transport in Rhodopseudomonas capsulata

Abstract

1. The effects of varying the ambient oxidation/reduction potential on the redox changes of cytochromes c, cytochromes b and P605 induced by a laser flash in chromatophores from Rhodopseudomonas capsulata Ala Pho + have been investigated. 2. The appearance and attenuation of the changes with varying ambient redox potential show that, of the cytochromes present, cytochromes c with Em 7 = 340 mV and 0 mV, and cytochrome b, Em 7 = 60 mV were concerned with photosynthetic electron flow. 3. The site of action of antimycin was shown to be between cytochrome b 60 and a component, as yet unidentified, called Z. 4. The appearance or attenuation of laser-induced changes of cytochromes c 0 and b 60 on redox titration was dependent on pH, but no effect of pH on the cytochrome c 340 titration was observed. 5. The dependence on ambient redox potential of the laser-induced bleaching at 605 nm enabled identification of the mid-point potentials of the primary electron donor ( Em 7 = 440 mV) and acceptor ( Em 7 = −25 mV). 6. The interrelationship of these electron carriers is discussed with respect to the pathway of cyclic electron flow.