El corazón púrpura de la fotosíntesis

The structure of a photosynthetic complex from a purple bacterium reveals a new class of light-harvesting protein and the channels that might allow electron-transporting molecules to escape this otherwise closed system.

Light-harvesting complex 2 (LH2) contains two groups of bacteriochlorophyll (BChL) pigments, B800 and B850. Light energy absorbed by B800 is transferred to B850 (blue arrows). It is then passed to another group of BChLs (B880) in light-harvesting complex 1 (LH1), and finally into the reaction centre (RC). The excited RC fully reduces ubiquinone molecules (Q), which leave the LH1–RC complex and pass into the membrane, transferring electrons (e⁻) to the cytochrome bc₁ complex; this transfer forms part of a cyclic electron-transport pathway (red arrows) that drives photosynthesis. This pathway is completed by a soluble protein, cytochrome c₂ (Cyt c₂). The periplasm is the region between the cell membrane and the cell wall of the bacterium.

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