Molecular biology of photosynthetic bacteria

The photosynthetic reaction center of purple bacteria is a multimeric, membraneassociated protein/chromophore complex. The function of the photosynthetic reaction center is to catalyze light-driven electron transfer across the photosynthetic membranes.

The photosynthetic reaction centers of purple bacteria have been well characterized, and all of them contain three subunits that are designated as L (light), M (medium), H (heavy). The designation of the subunits is based upon their apparent molecular masses as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis under denaturing conditions.

Photosynthetic reaction centers are also associated with light harvesting complexes, that absorb light energy and transfer it to the bacteriochlorophyll dimer ("special pair") that serves as the primary electron donor in the reaction center. The light harvesting complex is composed of (3 and a proteins, to which are bound pigment molecules.