Models of chromatophore organisation

The scheme shows two different concepts of the organization of the electron transfer chain in Rhodobacter sphaeroides. In the supercomplex model (left), all components of the chain are in supercomplexes, each containing 2 reaction centers (RC), 1 cyt c2, and 1 bc-complex.
In the model we favor (right), the RC, cyt c2 and bc-complex have the same relative overall stoichiometry (2:1:1), but are distributed at random in a population of chromatophores. Chromatophores are thought to contain, on average, 20-30 RC; for clarity, a smaller number is shown here. Heterogeneity in the distribution gives variable ratios of the different proteins in individual vesicles.
The redox enzymes are shown schematically, to indicate stoichiometries. The changes following a saturating flash assume that stigmatellin is present to limit the pool of donor electrons to 2 (cyt c2, cyt c1, but not FeS) per 2 RC.