Abstract
The mid-point potential (Em7.0) of the primary quinone acceptor (Qa) and the biochemical features (Em7.0 and apparent molecular mass, MM) of the membrane bound c-type cytochromes (cyt) involved in photosynthetic electron transfer of the halophilic phototrophic bacterium Rhodospirillum (Rs.) salinarum were determined. A tetrahemic RC bound cytochrome was found (MM of 39.8 kDa) with Em7.0 of the hemes equal to +304, +98, +21, −134 (± 8) mV as determined by dark equilibrium redox titrations in the isolated purified form. The highest potential heme (Em7.0 = +304 mV, α band at 556 nm) was able to reduce the photo-oxidized reaction center (P+) in a sub-millisecond (≤ 20 μs) time scale reaction, acting most likely as the direct electron donor to P+). The midpoint potential of the primary electron donor (Em7.0 = + 455 mV) was found to be close to that reported for the primary donor of the non-halophilic Rhodospirillum species Rs. rubrum, whereas the quinone primary electron acceptor (Qa) was different showing the spectral features of a menaquinone molecule with Em7.0 at −128 (± 5) mV. A membrane bound c-type heme with Em7.0 of 259 (± 1) and MM of 40 kDa was also isolated and referred to an orthodox cytochrome c1). The present data on the photosynthetic apparatus, along with the previous results on the respiratory system [Moschettini et al. (1997) Arch Microbiol 168: 302-309], suggest that Rs. salinarum is biochemically distinct from Rs. rubrum, the most representative specie of the genus.
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Moschettini, G., Bonora, P., Zaccherini, E. et al. The primary quinone acceptor and the membrane-bound c-type cytochromes of the halophilic purple nonsulfur bacterium Rhodospirillum salinarum: A spectroscopic and thermodynamic study. Photosynthesis Research 62, 43–53 (1999). https://doi.org/10.1023/A:1006319829120
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DOI: https://doi.org/10.1023/A:1006319829120