Rhodobacter sphaeroides photosystems

M. Losche, G. Feher, and M.Y. Okamura, The Stark Effect in Reaction Centers from Rhodobacter Sphaeroides R-26, Rhodopseudomonas Viridis and the D1D2 Complex of Photosystem II from Spinach, in "The Photosynthetic Bacterial Reaction Center", J. Breton and A. Vermeglio, eds.. Plenum Publishing Corp., San Diego (1988). 

Recently, the structures of the reaction centers from Rhodopseudomonas viridis and Rhodobacter sphaeroides have been solved at the atomic level (1,2). In both organisms the reaction center "core" polypeptides consist of the L and M subunits (responsible for charge separation), a cytochrome, and the H subunit (possibly required for stable assembly). It has become apparent that the bacterial reaction center, particularly the L and M subunits, can be directly compared to the reaction center polypeptides, D1 and D2, of Photosystem II (3). 

The crystallization of RCs in view of structure determination by x-ray crj taUography requires special methods that have worked successfully for two kinds of purple bacteria Rhodopseudomonas viridis and Rhodobacter sphaeroides) and for Photosystems I and II of thermophilic cyanobacteria. 

Gomelsky, M., Home, I.M., Lee, H.J., Pemberton, J.M., McEwan, A.G., and Kaplan, S., Domain structure, oligomeric state, and mutational analysis of PpsR, the Rhodobacter sphaeroides repressor of photosystem gene expression, /. Bacteriol, 182, 2253, 2000. 

The bacterial photosystem functions without dioxygen production which simplifies the task at hand. Namely, electrons are obtained from more easily oxidized terminal electron donors such as H2S instead of water. Nonetheless, the basic design needed to transform solar energy into stored chemical energy is present. The protein subunits and cofactors that comprise the photosystem in purple bacteria, such as Rhodobacter (Rb.) sphaeroides and Rhodopseudomonas (Rps.) viridis,33 are shown schematically in Fig. 1 which is based on a crystal structure of this assembly.34... 

Bacterial photosynthetic reaction centers (PRC) have been among the most actively studied ET proteins since DeVault and Chance first measured C. vinosum tunneling rates in the early 1960s. In many cases, measurements of ET kinetics preceded determination of the three-dimensional structure of the membrane-bound protein assembly. It was not until the X-ray crystal-stracture determinations of the Rhodopseudomonas (Rps.) viridus and Rhodobacter (Rb.) sphaeroides PRCs that distances could be assigned to specific rate constants. The recent crystal structures of photosystems l and from cyanobacteria promise to clarify critical aspects of the ET mechanisms in oxygenic PRC. ... 

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