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Figure 1.
Fig. 1. A representation of the major membrane proteins
involved in the light reactions of purple bacterial
photosynthesis. Photon energy (yellow arrows) captured by the
Bchla pigments (labeled B800 and B850 to indicate the
approximate wavelength in nanometers of maximal absorption) in
the antenna LH2 (purple) is passed to the LH1 Bchla (B880, red,
which also acts as a light-harvester), and then to a pair of
Bchla molecules (not shown) in the RC. Electron flow (red
arrows) occurs across the photosynthetic membrane from Bchla,
which is oxidized, to a primary electron acceptor, ubiquinone
(UQ[A], not shown), which is reduced. Subsequently, the electron
is transferred from UQ[A] to the secondary electron acceptor
ubiquinone (UQB, shown here as Q[B]). A second RC turnover
results in the complete reduction of UQ[B]^- to UQ[B]H[2]. The
fully reduced UQ[B]H[2] is replaced in the RC with an oxidized
ubiquinone (shown as Q) and passes its electrons to the next
redox component in the cyclic electron transport path, the
cytochrome b/c[1] complex (blue) (15). Electrons (e^-) are
returned to the RC through cytochrome c (Cyt c). A transmembrane
proton gradient is established and drives ATP synthase (orange),
producing ATP. ADP+Pi, adenosine diphosphate and inorganic
phosphate.
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