Posters P4Ab Type II reaction centres: Acceptor side. Abstracts (272-288)
Reconstitution of QB function with 1,4-naphthoquinone in bacteria reaction centers with different low potential QA's. Xinyu Zhang*,1, M. Gunner2, 1 The Graduate Center at City University of New York., New York, NY, USA2 Physics Department, City College of New York., New York, NY, USA
ABSTRACT- In the purple reaction centers from Rb. sphaeroides, ubiquinone is used at both primary (QA) and secondary (QB) sites, but they perform different functions. Many different quinones can functional at QA site, but no other quinone (XQ) will support electron transfer from XQA to XQB. In addition, ubi-QA has not been shown to easily reduce other quinones at QB. Previous work of Giangiacomo and Dutton (Proc. Natl. Acad. Sci. USA (1989)86, 2658-2662) showed that increasing the driving force between QA and QB site could allow reduction of non-native QBs. A low potential 2-methyl-3-Dimentylamino-1,4-Naphthoquinone (DMA-NQ) was synthesized. The binding affinity of DMA-NQ, Anthraquinone (AQ) and 1,4-Naphthoquinone (NQ) at QA are 0.06uM, 0.2uM and 8uM respectively. The quantum yield of the different quinones at QA site is 0.5, 0.9, and 1.0. The Em, relative to UQA is -423meV, -340meV, and 30meV. With an appropriate concentration of AQ or DMA-NQ and NQ, the low potential quinone is predominant occupant of QA while NQ is in the QB site. The KD of NQ for the QB site is around 20uM. The reaction kinetics slow as expected if there is electron transfer from QA– to QB. The back reaction rate with NQ at QB is 3.5s if DMA-NQ at QA, 2.1 s if AQ at QA. The reaction -GABo (DMA-NQ at QA and NQ at QB) = 248 meV; the reaction of -GABo(AQ at QA and NQ at QB) = 154 meV. Reduction of 1,4-naphthoquinone at QB is 240meV less favorable than with UQ at QB site. The Em of NQ is and 180mV lower than Ubiquinone at QA explaining why there is no electron transferred from UQA to NQ at QB. Supported by CREES 2003-02123.
KEY WORDS: electron transfer, bacteria reaction center, reaction rates, redox potential