Abstract
The reaction center complex from Rhodopseudomonas sphaeroides carotenoidless mutant R-26 has been well characterized as to its protein, pigment (4 bacteriochlorophylls (BChl) and 2 bacteriopheophytins (BPh)) and quinone content [ 11. The function of 3 or 4 of the pigment molecules as well as the quinones in the reaction center primary photochemistry is also becoming better understood [2,3]. Two of the BChls, the special pair, are believed to function as the primary electron donor on photoexcitation and transfer an electron to a ubiquinone molecule via one of the BPhs, which has been termed the intermediate electron acceptor. In addition, there is evidence that one of the remaining BChls is involved in the initial electron transfer from the special pair to BPh [3]. New spectroscopic methods are needed which can provide additional support to the picosecond optical absorption data, as well as structural information about the bonding interactions of BChl and BPh in the reaction center. finitive method for identifying the proposed transient intermediates in reaction center photochemistry. The vibrational spectrum of the BChl cation radical differs substantially from the neutral species [7,8]. We have undertaken a RR study of isolated Rps. sphaeroides reaction centers spontaneously adsorbed onto a Ag electrode: The advantages of studying the adsorbed complex include increased RR scattering intensity as a result of the surface enhanced effect on Ag [9], quenching of background fluorescence [lo], and the possibility of changing the redox state of the reaction center by varying the electrode potential.
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