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pH dependence of the charge recombination kinetics in bacterial RC reconstituted in liposomes

Published online by Cambridge University Press:  26 December 2018

Francesco Milano
Affiliation:
CNR−IPCF Institute for Physical and Chemical Processes, Via E. Orabona 4, I-70125 Bari, Italy
Livia Giotta
Affiliation:
Department of Biological and Environmental Sciences and Technologies, University of Salento, SP Lecce-Monteroni, I-73100 Lecce, Italy
Angela Agostiano
Affiliation:
Department of Chemistry, University of Bari “A. Moro”, Via E. Orabona 4, I-70125 Bari, Italy
Roberta Ragni
Affiliation:
Department of Chemistry, University of Bari “A. Moro”, Via E. Orabona 4, I-70125 Bari, Italy
Massimo Trotta*
Affiliation:
CNR−IPCF Institute for Physical and Chemical Processes, Via E. Orabona 4, I-70125 Bari, Italy
*
*To whom correspondence should be addressed [email protected]
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Abstract:

The photosynthetic Reaction Center from the carotenoidless mutant strain of the purple non sulphur bacterium Rhodobacter (R.) sphaeroides was reconstituted in artificial phospholipid vesicles (liposomes) to mimic the physiological membrane environment. The pH dependence in the interval 5 – 10 of the rate of the charge-recombination reactions from the final electron acceptors QA and QB to the primary electron donor (namely kAD and kBD) have been investigated. The liposomes were constituted of either the zwitterionic phosphatidylcholine (PC) or the negatively charged phosphatidylglycerol (PG), two of the main phospholipids found in the photosynthetic membrane of the bacterium. In both cases, the kAD has no pH dependence similarly to the detergent case. The kBD also has a pH dependence similar to the detergent case, having two distinct regions below pH 7 and above pH 9. Fitting of the titration curve to a function involving two protonation sites results in a marked shift of the pKAs between the different solubilizing environments. These differences are discussed in the frame of possible physiological implications.

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Articles
Copyright
Copyright © Materials Research Society 2018 

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